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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Vapor-liquid-solid (VLS) growth of tin dioxide (SnO2) nanowires (NWs) on the c-plane sapphire substrate coated with the Au film (5-30 nm in thickness) was performed by atmospheric-pressure CVD utilizing alternate source supply (ASS) of tin (Sn) and water (H2O). X-ray diffraction measurements and scanning electron microscope (SEM) observations revealed the successful growth of SnO2 NWs by the ASS technique. The ASS technique was found to be effective for suppressing the enhancement of the NWs average diameter caused by the increase in growth temperature (T-g). In the cycle number range from 300 to 800, the NWs average diameter was almost independent of cycle number, indicating that the radial growth due to vapor-solid (VS) growth was suppressed. PL spectra of the NWs were dominated by a broad orange band (OB) emission (similar to 1.9 eV) associated with oxygen vacancy (V-O) and/or interstitial tin atom (Sn-i). Mirror reflection symmetry between the PL and PLE spectra with a very large Stokes shift indicated a strong coupling between the deep-level defect and phonons in the optical transition process. The enhancement of the OB emission with increasing T-g is probably due to the increase in the density of the structural defects composed of V-O and/or Sni. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2017.05.053

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Possibility of selective growth of polycrystalline CuO and Cu2O films on the Au/SiO2/Si(100) substrates by chemical bath deposition (CBD) based technique using Cu(NO3)(2)center dot 3H(2)O (abbreviated as "CuNit") as a Cu precursor was investigated. The CuO films synthesized from the aqueous solutions of CuNit with pH adjusted to be in the range from 6.0 to 11 were composed of the corncob-like nanorods whose average diameter increased with increasing pH. For the CuO films synthesized from the CuNit aqueous solutions with pH > 10.5, the corncob-like nanorods were self-organized in the caddis clew-like shapes. The Cu2O films were synthesized mainly from the mixed aqueous solutions of CuNit and C6H12N4 (denoted by "HMT") with the assistance of a piece of iron (Fe) plate immersed in the solution but without applying any electric field (denoted by "Fe-assisted CBD" as distinguished from the usual CBD). Oxidation-reduction potential measurements revealed that the mixed aqueous solutions of CuNit and HMT in which the Fe plate was immersed had high concentration of electrons, contributing to the reduction of Cu2+ ions to Cu+ ions. At the beginning of the deposition, the Cu2O film composed of the triangular grains was oriented towards the [111] direction. The increase in growth time resulted in the enhancement of the contribution of the pyramidal grains oriented towards the [100] direction. By increasing the concentration of the mixed aqueous solution of CuNit and HMT, the preferential growth direction was changed continuously from the [111] direction to the [100] direction, accompanied with the change in grain shape from the triangle to the four-sided pyramid. It was also confirmed that the Cu2O films can be synthesized from the CuNit solutions by the Fe-assisted CBD when the pH value of the solution is adjusted to be in the range pH 4.7 to 5.1. However, the use of the CuNit solution with pH higher than 6.2 led to the coexistence of Cu2O and Cu(OH)(2) or the appearance of the single phase CuO in the film.

DOI： 10.1016/j.tsf.2017.08.054

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Growth experiments of monoclinic gallium oxide (beta-Ga2O3) nanostructures were performed by the atmospheric-pressure CVD using metal gallium (Ga) beads and water (H2O) as source materials and a Au film as a catalyst in terms of substrate materials, Au film thickness, growth temperature and growth time. Local structure analysis based on transmission electron microscope (TEM) observations and selective area electron diffraction (SAED) measurements revealed the successful growth of single crystalline beta-Ga2O3 nanowires (NWs) through vapor-liquid-solid (VLS) growth mechanism. The average diameter of the NWs was changed in the range from similar to 60 to similar to 1500 nm under the growth conditions picked up in this paper. The critical temperature for the VLS growth using the 30 nm-thick Au catalytic film was experimentally estimated to be similar to 789 degrees C. The diversity of shapes of nanostructures was probably due to the temperature evolution of Au catalytic particle size, the film growth on the NW sides by vapor-solid (VS) growth mechanism, and the epitaxial relation between the substrate and the individual NW. The photoluminescence intensity of the blue band emission at similar to 490 nm relative to that of the ultraviolet band emission at similar to 360 nm became larger with increasing average diameter, suggesting the increase in the native defects formed near the surface region. (C) 2016 Published by Elsevier B.V.

DOI： 10.1016/j.tsf.2016.07.074

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Vertically aligned zinc oxide (ZnO) nanorods (NRs) were successfully grown on Au/alkali-free glass substrates by chemical bath deposition (CBD) using themixed aqueous solution of zinc nitrate hexahydrate [Zn(NO3)(2)center dot 6H(2)O] and hexamethylenetetramine (HMT) (denoted by "ZnNit solution"). Even if both the growth time and growth temperature were constant, both the diameter and length of the NRs increased with increasing the concentration of the ZnNit solution. The ZnO NRs grown from the ZnNit solutions with the high concentrations exhibited a strong near-band-edge emission on their PL spectra, indicating their high crystalline quality. Using two different types of substrate holders realizing the different substrate configurations in the ZnNit solution, ZnO NRs standing perpendicular to the CuO surface or inclined with respect to the normal of the CuO surface were obtained on the CuO films prepared by CBD using the aqueous solution of copper (II) nitrate trihydrate [Zn(NO3)(2)center dot 3H(2)O]. The CBD experiments of ZnO NRs/CuO heterostructures were performed by using the ZnNit solutions with different concentrations in the range of 0.01-0.1M. Remarkable differences between the NRs grown using the two different substrate holders can be observed on the densities and the average diameters of the NRs, but not on the average lengths of the NRs. This finding suggests that the configuration of the substrate in the ZnNit solution during the deposition process is one of the important factors for controlling the shapes of the NRs as well as the concentration of the solution. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2015.07.082

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Structural properties of highly c-axis oriented polycrystalline Ga-doped ZnO (GZO) films prepared by ion plating with a DC arc discharge were studied in terms of the oxygen gas flow rate (F-O2) introduced into the chamber during the deposition process and the Ga2O3 content in the GZO sintered pellet The X-ray diffraction (XRD) measurements revealed that the GZO films have the residual compressive stress along the a-axis direction (in plane) and he tensile stress along the c-axis direction (out-of-plane). The increase in F-O2, or the increase in Ga2O3 content was effective for relaxing the in plane compressive stress induced by the so-called atomic peening effect. The positive correlation between the carrier concentration (n) and the primitive cell volume (V) would be clue to the incorporation of Ga atoms substituting Zn sites (Ga(Zn)s) together with the generation of n-type intrinsic defects or complex defects. (C) 2015 Elsevier B.V. All rights reserved

DOI： 10.1016/j.tsf.2015.08.056

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.1.0_3826

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Structural and electrical properties of the CuO films and the ZnO/CuO heterojunctions prepared by chemical bath deposition (CBD) technique involving thermal annealing process were studied by scanning electron microscope observation, X-ray diffraction, current density-voltage (J-V) and capacitance-voltage (C-V) measurements. The as-grown CuO films showed p-type conduction after annealing in the air at temperatures (T-A) ranging from 200 to 300 degrees C. The n-ZnO/p-CuO heterojunctions were composed of the columnar CuO grains and the ZnO nanorods (NRs) and their J-V curves exhibited rectifying characteristics with large diode ideality, factors (n) and leakage currents. The insertion of the ZnO intermediate layer prepared by dip-coating (denoted by "Dip-coating ZnO") between the ZnO and CuO layers was found to be effective for reducing the n value and suppressing the leakage current. The threshold voltage (V-th), built-in potential (V-bi) and n value of the ZnO/Dip-coating ZnO/CuO heterojunction were strongly dependent on T-A and showed minima around T-A=250-300 degrees C. Taking into account the fact that the rectification ratios of the forward current to the reverse current were very low at the same T-A region, the low V-th and V-bi values are attributed to the tunneling process through the interface states introduced by the structural imperfection. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.solmat.2014.08.023

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Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on alpha-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)(2)). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (I-UV) to the latter emission (I-VIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70 degrees C to 90 degrees C, the molarity dependences of I-UV/I-VIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm(2)/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 x 10(17) cm(-3) grown from the aqueous solution of 40 mM at 70 degrees C.

DOI： 10.1186/s11671-014-0715-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (IUV) to the latter emission (IVIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of IUV/IVIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm2/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 1017 cm−3 grown from the aqueous solution of 40 mM at 70°C.

DOI： 10.1186/s11671-014-0715-0

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：VERLAG DR KOSTER  

Films and nanostructures of beta-Ga2O3 were successfully grown by atmospheric-pressure CVD (AP-CVD) using metal Ga and H2O as source materials. It was confirmed that highly (-201) oriented polycrystalline beta-Ga2O3 films can be obtained on c-plane sapphire (c-Al2O3) substrates by optimizing growth temperature (T-g) and source supply ratio of H2O to Ga. The optical gap energy of the beta-Ga2O3 film with a relatively flat surface was estimated to be similar to 4.9 eV. Photoluminescence (PL) measurements for the beta-Ga2O3 films revealed the existence of at least three emission bands with their peaks at similar to 370 nm, similar to 440 nm and similar to 520 nm. Various shapes of quasi 1D nanostructures, such as nanowires (NWs), nanorods (NRs), tapered NRs and nanobelts (NBs), were obtained on the c-Al2O3 substrates coated with the Au films by utilizing vapour-liquid-solid (VLS) growth mechanism. The diversity of the quasi 1D nanostructures is probably due to the contribution of vapour-solid (VS) growth mechanism and/or the coalescence between the neighbouring Au metal particles before initiating the NW (or NR) growth. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201510012

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Temperature dependent Hall effect measurements were performed for the undoped CdO films with carrier concentrations (n) ranging from 2.4 x 10(19) to 2.0 x 10(20) cm(-3) grown on c- and r-plane sapphire substrates by the atmospheric-pressure chemical vapor deposition using Cd powder and H2O as source materials. The n dependence of the optical gap energy (E-opt) could be explained by the combination of the band gap widening due to Burstein-Moss shift and the band gap shrinkages due to the electron-electron and electron-impurity interactions. For all the films, the carrier concentrations (n) were independent of measurement temperature (T), indicating that these films were n-type degenerate semiconductors. The barrier heights at grain boundaries determined from the 1000/T-ln(mu T) curves were smaller than the thermal energy at 300 K, suggesting that the grain boundary scattering plays a minor role on the carrier transport in comparison with the intra-grain scattering. The n dependence of the gradient of the mu-T curve revealed the continuous transformation of the dominant intra-grain scattering mechanism from the phonon scattering to the ionized impurity scattering with increasing n. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2014.07.061

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Temperature dependent Hall effect measurements were performed for the undoped CdO films with carrier concentrations (n) ranging from 2.4 x 10(19) to 2.0 x 10(20) cm(-3) grown on c- and r-plane sapphire substrates by the atmospheric-pressure chemical vapor deposition using Cd powder and H2O as source materials. The n dependence of the optical gap energy (E-opt) could be explained by the combination of the band gap widening due to Burstein-Moss shift and the band gap shrinkages due to the electron-electron and electron-impurity interactions. For all the films, the carrier concentrations (n) were independent of measurement temperature (T), indicating that these films were n-type degenerate semiconductors. The barrier heights at grain boundaries determined from the 1000/T-ln(mu T) curves were smaller than the thermal energy at 300 K, suggesting that the grain boundary scattering plays a minor role on the carrier transport in comparison with the intra-grain scattering. The n dependence of the gradient of the mu-T curve revealed the continuous transformation of the dominant intra-grain scattering mechanism from the phonon scattering to the ionized impurity scattering with increasing n. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2014.07.061

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The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75 degrees C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm(2) and temperatures above 80 degrees C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75 degrees C with a low current density of -0.1 mA/cm(2) exhibited the highest density of 1.45 x 10(9) cm(-2). X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, IUV/IVIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm(2) showed high IUV/IVIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.

DOI： 10.1186/1556-276X-9-609

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

Electrical properties of n-ZnO/p-CuO heterojunctions prepared by chemical bath deposition were investigated. The insertion of intermediate layer, such as ZnO layer grown by dip-coating, was found to be effective for suppressing leakage current. For the ZnO/Dip-coating ZnO/CuO heterojunctions, the threshold voltage V_<th> and ideality factor n of the J-V curve and the built-in potential V_<bi> determined from the C-V curve had minima around the post-annealing temperature for CuO layer (T_A) of 250℃. Relatively low I_F/I_R values (I_F: forward current, I_R: reverse current) at T_As higher than T_A=225℃ suggest the contribution of the tunnel current through the defect states to the reduction of the V_<th> and V_<bi>.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm2 and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm2 exhibited the highest density of 1.45 × 109 cm-2. X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, IUV/IVIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm2 showed high IUV/IVIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.

DOI： 10.1186/1556-276X-9-609

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Ga-doped ZnO (GZO) films with carrier concentrations ranging from 5.2 x 10(17) to 2.9 x 10(20) cm(-3) were grown on r-plane sapphire substrates by atmospheric-pressure CVD (AP-CVD). The gradients of Hall mobility (mu) - temperature (T) curves (denoted by Delta mu/Delta T) for the GZO films grown by AP-CVD (CVD-GZO films) plotted as a function of carrier concentration n obey those for the GZO films deposited by ion plating with dc arc discharge (IP-GZO films). This suggests that the dominant carrier scattering mechanism limiting the carrier transport is common between the CVD-GZO and IP-GZO films at any given n. The CVD-GZO films with low n exhibited the Ga-related neutral donor bound exciton and two-electron satellite (TES) lines at low temperature. With increasing n, the above two characteristic lines shifted higher energies accompanied by broadening. The IP-GZO films exhibited two emission lines with opposite n dependences; with increasing n, one line shifted towards higher energies, whereas another line shifted towards lower energies. With an increase in n caused by the donor doping, the relaxation of the momentum-conservation law brought the remarkable changes to the PL and PLE spectra of both the IP-GZO and CVD-GZO films with n of more than 4.0 x 10(19) cm(-3) that is close to the Mott density. (C) 2013 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.tsf.2013.06.039

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Zinc oxide (ZnO) nanorods (NRs) were synthesized on glass substrates and Au seed layers by chemical bath deposition from the aqueous solution of ZnCl2 and the mixed aqueous solution of zinc acetate dihydrate (ZnAc) and hexamethylenetetramine (HMT) at a low temperature of similar to 90 degrees C. Vertically aligned NRs were successfully grown on the Au seed layers. For the NRs synthesized from the ZnCl2 solution of 0.17 M, when the growth time increased from 15 to 180 min, the average diameter and length increase from similar to 350 to similar to 1020 nm and from similar to 1000 to similar to 5600 nm, respectively. The increase in average diameter with the concentration of solution was observed on the NRs synthesized from the mixed solution of ZnAc and HMT. The influence of additional HMT was found on the shapes and density of the NRs. Photoluminescence (PL) spectra of the NRs synthesized from the solutions of ZnCl2 exhibited a dominant orange band (OB) emission at similar to 640 nm associated with the excess-oxygen atoms. On the other hand, the NRs synthesized from the mixed solution of ZnAc and HMT exhibited a strong near-band-edge (NBE) emission at similar to 380 nm, suggesting their high crystalline quality. For the NRs synthesized from the mixed solution of ZnAc and HMT, the OB emission is effectively excited at the photon energy corresponding to the A free exciton emission. For the NRs synthesized from the solution of ZnCl2, however, the secondary phase Zn(OH)(2) formed at the surface regions of the NRs contributes to the excitation process for the OB emission. Photoacoustic (PA) measurements revealed that the intra-band-gap absorption band extending from 400 to 660 nm responsible for nonradiative transitions were suppressed in the NRs synthesized from the mixed solutions of ZnAc and HMT in comparison with those from the ZnCl2 solutions. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2013.05.174

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Optical properties of ZnO films and nanorods (NRs) grown by atmospheric-pressure CVD (AP-CVD) and chemical bath deposition (CBD) were studied by photoluminescence (PL), photoluminescence excitation (PLE) and photoacoustic (PA) measurements. Visible emissions from the samples were classified into three groups
a green band (GB) at ~2.34 eV, an orange band (OB) at ~1.97 eV and a red band (RB) at ~1.77 eV. Regardless of precursor, PL spectra of the CBD NRs were dominated by the OB. However, PLE measurements revealed that the difference in precursor resulted in the difference of the excitation process for the OB. The PLE spectrum for the RB exhibited the excitation bands at 2.75-3.18 eV and 1.91-2.48 eV. The former was also observed on the PLE spectrum for the GB, suggesting that the same defect or impurity states contribute to both the GB and RB. The PA spectra of the NRs synthesized by CBD from the mixed aqueous solution of Zn(CH3COO)22H2O and C6H12N4 exhibited the decrease in intra-band-gap-absorption with increasing solution concentration. For the AP-CVD Ga-doped ZnO films, when the carrier concentration (n) increased from 5.2×1017 to 7.2×1019 cm-3, the difference between PLE and PL peak energies (EPLE-EPL) decreased slightly. This is probably due to the broadening of the Ga-related impurity level, followed by merging with the edge of the conduction band. Above n =9.5×1019 cm-3, the EPLE-EPL increased rapidly with increasing n, resulting from the filling of the tail states and lower parts of the conduction band. © 2013 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201300174

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Morphological, electrical and optical properties of undoped and Ga-doped ZnO and undoped CdO films grown on sapphire (Al2O3) substrates by the atmospheric-pressure CVD method using Zn, Cd, H2O and GaCl3 as source materials were investigated. The influences of the deviation from the stoichiometric composition were clearly observed on photoluminescence (PL), photoluminescence excitation (PLE) and photoacoustic (PA) spectra of the undoped ZnO films. The carrier concentration n in the undoped ZnO film was found to be dominated by the hydrogen related donors rather than native defects. The Ga doping in ZnO film led to the degradation of surface flatness, the increase in carrier concentration n and the decrease in Hall mobility μ. With increasing carrier concentration n, the Ga-related neutral donor bound exciton line of the Ga-doped ZnO film shifted towards shorter wavelengths, accompanied by asymmetric broadening. This is probably due to the screening of the Coulomb potential by heavily introduced donors and free-electrons. Highly oriented CdO films with smooth surfaces were successfully grown on r-Al2O3 substrates. Transmittance values for the CdO/r-Al2O3 films were higher than 70% in the range of 700-2500nm. Under the assumption that the reflectance is neglected, the direct and indirect optical gap energies of the CdO films determined from the transmittance spectra were 2.34-2.38eV and 1.98-2.06eV, respectively. PA measurements for the CdO films revealed that the tail states associated with the residual impurities and/or the structural defects reduce the direct optical gap energy. A maximum Hall mobility μ of 178cm2/Vs was achieved on the CdO/r-Al2O3 film with the carrier concentration n of 4.2×1019cm-3. © 2013 Elsevier B.V.

DOI： 10.1016/j.surfcoat.2013.06.015

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Cadmium oxide (CdO) nanostructures of various shapes were successfully grown on gold (Au) nanocolloid coated c-plane sapphire substrates by atmospheric-pressure CVD using Cd powder and H2O as source materials. CdO nanorods (NRs) exhibited tapered shapes and the degree of the tapering became larger with increasing substrate temperature. One of the possible reasons for the tapering behavior is the competition between the axial growth due to the vapor-liquid-solid (VLS) mechanism and the radial growth due to the vapor-solid (VS) mechanism. The influence of the competition between the two different growth mechanisms was also confirmed on the appearance of "seaweed-like" NRs. Moreover, we cannot neglect the influence of the shrinkage of catalyst particles during the growth process on the tapering behavior. In addition, there is a possibility that the temporal evolution of catalyst particles, such as diffusion, splitting, migration and coalescence, contributes not only to the disappearance of catalyst particles on the tips of the NRs, resulting in the enhancement of the radial growth relative to the axial growth, but also to the formation of nanobelts (NBs) and nanotrees (NTs). Photoacoustic measurements revealed that the absorption edge shifts towards lower energies and the absorption band below the absorption edge becomes larger with increasing TS. This tendency may be due to the increase of intrinsic defects and/or the decrease in residual impurities. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2012.08.061

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Ga-doped ZnO (GZO) films with carrier concentration n ranging from 3 x 10(18) to 1.04 x 10(21) cm(-3) were deposited by ion plating with DC arc discharge. The results of Hall effect measurements of the GZO films revealed that the gradients of Hall mobility (mu)-temperature (T) curves (denoted by Delta mu/Delta T) plotted as a function of n can be divided into three regions: (1) Region I (3 x 10(18) < n < 4 x 10(19) cm(-3)); Delta mu/Delta T > 0 and mu decreasing with increasing n, (2) Region II (4 x 10(19) < n < 3 x 10(20) cm(-3)); mu independent of T (Delta mu/Delta T = 0) and (3) Region III (n > 3 x 10(20) cm(-3)); Delta mu/Delta T<0. For all GZO films, the activation energies extracted from the 1000/T-ln (mu T) curves were lower than the thermal energy k(B)T at 300 K, indicating that the carrier electrons can overcome the potential barriers at grain boundaries. Moreover, comparison of the calculated mean free path l of the carrier electrons and the depletion layer width at the grain boundaries showed that the grain boundary scattering mechanism plays a minor role in the carrier transport compared with the intra-grain scattering mechanism for GZO films with n higher than 3 x 10(18) cm(-3). The dependence of Delta mu/Delta T on n demonstrates the continuous transformation of the dominant intra-grain scattering mechanism from the ionized impurity scattering mechanism to the phonon scattering mechanism with increasing n. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2012.07.140

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Zinc oxide (ZnO) NRs were successfully grown by the chemical bath deposition (CBD) using ZnCl_2 aqueous solution. The shapes of the vertically aligned NRs on the gold (Au) seed layers changed from cones to hexagonal prisms with increasing ZnCl_2 content. With increasing growth time (t_g), both the diameter and length increased, and the distance between the neighboring NRs decreased, resulting in the systematical change from the NRs array to the film. Photoluminescence (PL) and photoluminescence excitation (PLE) measurements for as-grown and annealed NRs revealed that the surfaces of the as-grown NRs are in oxygen excess and contain the secondary phase of Zn(OH)_2. The fabrication of n-type ZnO NRs/p-type Cu-O NRs hetero-junctions was also performed by the CBD based technique.

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

Various shapes of nanostructures of oxide materials ZnO, CdO and MgO have been obtained by atmospheric-pressure chemical vapor deposition methods using Au nanocolloids as catalyst. Shapes of ZnO and CdO nanorods (NRs) changed from cylinders to cones with increasing substrate temperature, so-called "tapering". It was confirmed for the ZnO NRs that the alternate source supply of Zn and H_2O is effective for suppressing the tapering behavior. The ZnO NRs were also successfully grown on sprayed (MgZn)O seed layers by the solution growth (SG) using the aqueous solution of Zn(CH_3COO)_22H_2O. It was found that the averaged diameter of the SG-ZnO NRs increased with the increase in concentration of the solution.

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J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Various shapes of ZnO and CdO nanostructures were successfully grown on a-and c-plane sapphire substrates coated with Au nanocolloidal solution by atmospheric-pressure chemical vapor deposition methods under a simultaneous source supply of metal powder (Zn or Cd) and H2O. The ZnO and CdO nanorods (NRs) grown at higher substrate temperatures (T(S)s) exhibited tapered shapes, resulting from the competition between the axial growth due to the vapor-liquid-solid (VLS) mechanism and the radial growth due to the vapor-solid (VS) mechanism. The alternate source supply of Zn and H2O was found to be effective for suppressing the tapering of ZnO NRs. The appearance of the Y- and T-shaped nanotrees of CdO may be due to the splitting and migration of catalytic particles during the growth process. These results suggest that both the source supply sequence and the substrate temperature are important factors for the shape design of oxide nanostructures. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.01BJ15

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

Structural and photoluminescence (PL) properties of ZnO films grown by atmospheric pressure CVD methods using the sources of Zn(C5H7O2)(2)H2O (ZnAA) -C2H5OH, ZnCl2-C2H5OH and Zn-H2O, were compared. For the ZnAA-C2H5OH system, the influence of the crystalline imperfection was observed on the XRD pattern and the PL spectrum. RT PL spectrum of the highly c-axis oriented film grown on the a-plane sapphire substrate using ZnCl2-C2H5OH system exhibited a strong green band (GB) emission and a weak near-band-edge (NBE) emission. For the Zn-H2O systems, the c-and a-axis oriented films were successfully grown on the c-and r-plane sapphire substrates, respectively, and their PL spectra were dominated by the NBE emission. For the ZnCl2-C2H5OH system, only the variation of the PL intensity ratio of the GB emission to the NBE emission by changing the supply ratio of C2H5OH to ZnCl2 was observed. For the Zn-H2O system, however, the visible region PL changed from the red to the GB emission systematically by adjusting the supply ratio of H2O to Zn. The Zn-H2O system was found to be the most suitable for the defect control. Low temperature PL measurements revealed that the accurate control of the supply ratio of the O source to the Zn source is an important factor for controlling not only the defects, but also for the concentration of the residual impurities. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201000389

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Polycrystalline zinc oxide (ZnO) films were grown on alkali-free glass substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD) using diethylzinc (DEZn) and water (H2O) as precursors. Photoluminescence (PL) spectra of the films were composed of the near-band-edge (NBE) emission at similar to 380 nm and the orange band (OB) emission at similar to 600 nm. Variations of the intensity ratio of the NBE emission to the OB emission (I-NBE/I-OB) and the photon energy of the knee on the photoacoustic spectrum (PA edge) as a function of substrate temperature (T-S) could be divided into two regions at the boundary temperature (T-B). Below T-B, the NBE emission exhibited the tail extending to the higher energy than the bandgap of ZnO and the I-NBE/I-OB value became smaller with increasing T-S. In addition, the PA edge shifted towards lower energies with increasing T-S. Concerning the Raman results, these tendencies seem to have some relations with the decrease in concentration of the secondary phase Zn(OH)(2) with increasing T-S. Above T-B, however, the I-NBE/I-OB became larger and the PA edge shifted towards higher energies with increasing T-S, which is probably due to the removal of defect levels related to the excess oxygen atoms. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2010.06.061

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Chalcopyrite Cu(AlxGa1-x)S-2 alloy films were successfully grown on GaP substrates by vapor phase epitaxy using metallic chlorides (CuCl, GaCl3 and AlCl3) and H2S as source materials. Photoluminescence (PL) spectra of these films taken under a low excitation density using a super high pressure Hg lamp exhibited broad emissions in the orange region. Photoluminescence excitation (PLE) measurements revealed that these broad emissions are effectively excited at the photon energies of A- and the BC-exciton energies. Under the high excitation density using the pulsed XeCl laser, these alloy films showed the exciton related emissions composed of biexciton recombination, exciton-exciton and exciton-carrier scatterings. The influence of the compositional fluctuation was observed on the increase of the full-width at half maximum (FWHM) for the exciton related emission with increase in composition of x. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2010.03.021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

Films of ZnO have been grown on R-plane sapphire substrates by atmospheric-pressure chemical vapor deposition (AP-CVD) using Zn powder and H2O as source materials. Variation in growth rate as a function of substrate temperature can be divided into three regions: re-evaporation region, mass transport controlled region, and surface controlled region. Scanning electron microscope observations revealed that the surface morphology of the film is dependent not only on substrate temperature but also on Zn source and H2O source temperatures. X-ray diffraction patterns of most of the films showed a dominant (110) peak, indicating highly A-axis oriented growth. A single crystalline A-plane ZnO film without mixed domain was successfully grown by optimizing the growth condition. Visible region photoluminescence changed from orange-red emission to blue-green emission systematically by adjusting Zn source and H2O source temperatures. This result suggests the possibility of defect control in our AP-CVD system. For the films grown at T-S=700 degrees C in the mass transport controlled region, resistivity decreased from 0.45 to 0.007 Omega cm as TH2O rised from 54 to 75 degrees C.

DOI： 10.1116/1.3130157

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

Polycrystalline zinc oxide films were grown on glass substrates by low pressure metal organic chemical vapor deposition (LP-MOCVD) and metal organic molecular beam deposition (MOMBD) using diethlyzinc and water as precursors. With increasing substrate temperature (T-S), preferential growth direction of the LP-MOCVD films changed from c-axis direction to a-axis direction, while that of the MOMBD films changed from random direction to c-axis direction. Photoluminescence (PL) spectra of the LP-MOCVD films exhibited an orange band emission related to interstitial oxygen atoms, while those of the MOMBD films exhibited a green band emission related to oxygen vacancies. This PL result suggests that the LP-MOCVD films are in oxygen excess condition, but the MOMBD films are in oxygen deficient condition. Photoacoustic measurements revealed that the energy level of the nonradiative center formed in the LP-MOCVD films is deeper than that in the MOMBD films.

DOI： 10.1116/1.3130155

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A variety of vertically aligned ZnO nanostrutures, such as nanorods, pencil-like nanorods and nanowalls, was successfully grown on sapphire substrates coated with Au nanocolloidal solutions by atmospheric-pressure CVD using Zn powder and H2O as source materials. Shapes of the nanorods grown on the sapphire substrates coated with the diluted solution of enhanced metalorganic decomposition for NiO film depended strongly on degree of dilution of the solution. Possibility of diameter control using the Ni particles embedding in zeolite supports as catalytic material was also found. © 2009 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2009.78

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOC INC  

Photoluminescence spectra of polar ZnO/c-Al2O3 and non-polar ZnO/r-Al2O3 films grown by the atmospheric-pressure CVD using Zn and H2O as source materials have been investigated. For the non-polar films, the I-0, I-1 and I-2 lines on the high energy side of exciton-region were relatively strong. For the polar films, however, these emission lines were very weak. Moreover, several non-polar films exhibited the C-exciton emission. These differences between the polar and non-polar films are probably due to the difference in polarization selectivity resulting from the difference in growth direction. For both the polar and non-polar films, the 14 line attributed to the exciton bound to the H related donor increased with source supply ratio of H2O to Zn. For the non-polar films, the I-6, I-8 and I-9 lines attributed to the group III elements became weaker with increasing Zn source temperature suggesting the possibility of impurity doping under stoichiometry control.

DOI： 10.1149/1.3207591

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AVS Science and Technology Society  

Films of ZnO have been grown on R -plane sapphire substrates by atmospheric-pressure chemical vapor deposition (AP-CVD) using Zn powder and H2 O as source materials. Variation in growth rate as a function of substrate temperature can be divided into three regions: re-evaporation region, mass transport controlled region, and surface controlled region. Scanning electron microscope observations revealed that the surface morphology of the film is dependent not only on substrate temperature but also on Zn source and H2 O source temperatures. X-ray diffraction patterns of most of the films showed a dominant (110) peak, indicating highly A -axis oriented growth. A single crystalline A -plane ZnO film without mixed domain was successfully grown by optimizing the growth condition. Visible region photoluminescence changed from orange-red emission to blue-green emission systematically by adjusting Zn source and H2 O source temperatures. This result suggests the possibility of defect control in our AP-CVD system. For the films grown at TS =700 °C in the mass transport controlled region, resistivity decreased from 0.45 to 0.007 cm as T H2 O rised from 54 to 75 °C. © 2009 American Vacuum Society.

DOI： 10.1116/1.3130157

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AVS Science and Technology Society  

Polycrystalline zinc oxide films were grown on glass substrates by low pressure metal organic chemical vapor deposition (LP-MOCVD) and metal organic molecular beam deposition (MOMBD) using diethlyzinc and water as precursors. With increasing substrate temperature (TS), preferential growth direction of the LP-MOCVD films changed from c -axis direction to a -axis direction, while that of the MOMBD films changed from random direction to c -axis direction. Photoluminescence (PL) spectra of the LP-MOCVD films exhibited an orange band emission related to interstitial oxygen atoms, while those of the MOMBD films exhibited a green band emission related to oxygen vacancies. This PL result suggests that the LP-MOCVD films are in oxygen excess condition, but the MOMBD films are in oxygen deficient condition. Photoacoustic measurements revealed that the energy level of the nonradiative center formed in the LP-MOCVD films is deeper than that in the MOMBD films. © 2009 American Vacuum Society.

DOI： 10.1116/1.3130155

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Zinc oxide (ZnO) films grown by atmospheric-pressure chemical vapor deposition using Zn powder and water (H2O) as source materials were investigated by photolurnmescence (PL), photoacoustic (PA), Raman scattering, infrared (IR) absorption and attenuated total reflection (ATR) measurements. PL results suggested that the concentration of oxygen vacancy (V-O) can be controlled by adjusting the source feed ratio Of H2O to Zn (VI/II). PA measurements revealed that an absorption edge shifted to lower energies with increasing VIAL It was also found that the increase in VI/II contributed to the decrease in resistivity. Raman, IR absorption and ATR spectra showed that the films contained high concentrations of hydrogen atoms. There is a possibility that the increase in concentration of hydrogen related donors contributes to both the VI/II dependence of PA spectrum and that of resistivity. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2007.06.130

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Highly oriented ZnO films have been grown on c-plane sapphire substrate by atmospheric-pressure chemical vapor deposition using Zn powder and H2O as source materials, Photoluminescence intensity ratio of the green band at similar to 2.5 eV to the near-band-edge emission at similar to 3.2 eV (I-GB/I-NBE) decreased with increasing the source feeding ratio of H2O to Zn (VI/II), indicating the possibility of the defect control. The absorption edge of the photoacoustic spectrum shifted towards lower energies and the resistivity decreased with increasing VI/II ratio. These tendencies are related to the incorporated H atom, the existence of which was confirmed by Raman, infrared absorption and attenuated total reflection measurements. Nanowires (NWs) of ZnO were successfully grown on the SiO2/Si(100) substrate coated with the An nanoparticle solution or the solution for enhanced metalorganic decomposition for NiO film. The diameters of NWs grown by the former and the latter solutions changed from 50 to 250 nm and from 60 to 700 nm depending on substrate temperature and concentration of the solution, respectively. Several NWs grown on the patterned Si substrate with line-and-space pattern bridged between the mesas. Moreover, suspended NWs were grown between the Si cylindrical pillars. These results demonstrate the possibility of self-assembling nano-interconnection. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2007.04.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Structural, optical and electrical properties of polycrystalline Cu-In-Se films, such as CuInSe2 and ordered vacancy compounds (OVC), prepared by three-stage process of sequential chemical spray pyrolysis (CSP) of In-Se (first stage), Cu-Se (second stage) and In-Se (third stage) solutions have been studied in terms of substrate temperature at the second stage (T-S2). The films grown at T-S2 <= 420 degrees C exhibited larger grains in comparison with the Cu-In-Se films grown by the usual CSP method. Optical gap energy was approximately 1.06 eV for 360 degrees C <= T-S2 <= 420 degrees C, but increased dramatically from 1.06 to 1.35 eV when the T-S2 rose from 420 to 500 degrees C. Conductivity type was p-type for T-S2 < 420 degrees C, but n-type for T-S2 > 420 degrees C. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.solmat.2006.06.063

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Growth of ZnO films was carried out on the c-plane sapphire (alpha -Al2O3 (0 0 0 1)) and glass substrates by metalorganic molecular beam epitaxy (MOMBE) using diethylzinc (DEZn) and H2O as source precursors. The lattice constant c of the ZnO/alpha-Al2O3 (0 0 0 1) layer decreased with increasing feeding ratio of H2O to DEZn (VI/II ratio). Photouminescence (PL) intensity ratio of the green band to the near-band-edge (NBE) emission (I-GB/I-NBE) became smaller with increasing VI/II ratio. These results are probably due to the decrease in oxygen vacancy concentration. Highly c-axis-oriented polycrystalline ZnO films were grown at T-S >= 300 degrees C under VI/II = 25. The full-width at half-maximum (FWHM) value of the (002) diffraction peak was minimum at T-S = 300-375 degrees C. The I-GB/I-NBE ratio for the polycrystalline ZnO/glass film showed minimum value at T-S = 300 degrees C. The quality of the ZnO/glass film was best at T-S = 300-375 degrees C, which is lower in comparison with the ZnO/alpha-Al2O3 (0 0 0 1) layer. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2006.10.063

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Structural and optical properties of In-rich Cu-In-Se polycrystalline thin films (0.54 < In/ (Cu + In) < 0.78) prepared by chemical spray pyrolysis (CSP) on glass substrate have been systematically studied in terms of In/(Cu + In) ratio. Lattice constants a and c of the films decrease with increase of In/(Cu+In) ratio. The films exhibit a characteristic Raman peak shifting higher frequencies as the In/(Cu + In) ratio increases. Optical bandgap energy is approximately 1.22 eV for 0.54 < In/(Cu + In) < 0.67, but increases from 1.22 to 1.36 eV when the In/(Cu+In) ratio increases from 0.67 to 0.78. Photoacoustic measurements reveal the existence of high concentration of nonradiative centers introduced by the deviation from the stoichiometric composition. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.solmat.2005.03.010

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

Polycrystalline CuInS2 thin films were prepared by chemical spray pyrolisis (CSP) on glass sustrate from the ethanol aqueous solution containing CuCl2, InCl3 and thiourea. Structual, electrical and optical properties were systematically studied in terms of substrate temperature, pH and the ion ratio (Cu/In) of the spray solution. Although the In-rich films were composed of CuInS2 and In2S3, the In2S3 content in the film decreased with Cu/In ratio. Appearance of Raman peaks at 288 and 298 cm(-1) indicated that the films contained CuInS2 with chalcopyrite and CuAu phases. Typical grain size in the Cu-rich films was 200 nm. Optical gap energies were approximately 0.1-0.2eV smaller than the bandgap energy of the CuInS2 bulk crystal. Resisitivity of the Cu-rich films without In2S3 secondary phase was 0.2-5 Omega cm. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200669597

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

Polycrystalline Mg(x)Z(1-x)O (0.00 <= x <= 0.21) and ZnO:Mn films prepared by chemical spray pyrolysis were characterized by X-ray diffraction, optical transmittance, photoacoustic (PA) spectroscopy and photoluminescence (PL). Successful growth of the MgxZn1-xO (0.00 <= x <= 0.21) films was confirmed by the blue shift of both the near-band-edge PL peak and absorption edge with increasing the alloy composition x. However, the influence of the tail states caused by the deviation from stoichiometric compsosition and/or the spatial fluctuation of the alloy composition x was observed on the PA and PL spectra. Both the transmittance and PA spectra for the ZnO:Mn films showed the absorption band due to the d-d transitions in Mn2+ ion. (c) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200669599

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

CuIn(SxSe1-x)(2) thin polycrystalline films were grown by the chemical spray pyrolysis method on the glass substrate at 280-400 degrees C. The alloy composition in the film was studied with relation to that in the splay solution. Films were characterized by X-ray diffraction, optical absorption, Raman spectroscopy, resistivity and surface morphology. The CuInSe2-rich alloy films grown at high substrate temperature had chalcopyrite structure, while, the CuInS2-rich films grown at low substrate temperature exhibited sphalerite structure. Optical-gap energies were smaller than that of the bulk crystal by 0.1-0.2 eV for CuInS2-rich films. Raman spectra exhibited both CuInSe2-like and CutnS(2)-like A(1) modes, and their relative changed systematically with alloy composition. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.09.091

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Raman spectra for non-site-selectively and site-selectively Zn-doped CuGaS2 layers grown by vapor phase epitaxy (VPE) were investigated. Although an appearance of characteristic Raman line(s) related with the doped Zn atom was not seen, an enhancement of the Raman intensity ratio of the highest LO mode to the A(1) mode (I-LO/I-AI) was observed. The site-selectively Zn-doped layers with p-type conductivity exhibited larger I-LO/I-AI ratio compared to those with n-type conductivity. The observed correlation between the I-LO/I-AI ratio and the peak energy of the photoluminescence characteristic for Zn-doped p-type samples (L emission) suggests that the enhancement of I-LO/I-AI is due to the increase of Zn atom substituting Ga site (Zn-Ga) which is acting as an acceptor. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.09.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Single crystalline ZnO nanowires (NWs) with diameters ranging from 80 to 700 nm were successfully grown on Ni-coated SiO2/Si(100) substrates by atmospheric pressure chemical vapor deposition (CVD) using ZnCl2 and H2O as source materials. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations revealed that the ZnO NWs grown by two types of CVD systems with different source feeding configurations exhibited different morphologies and growth directions, reflecting the difference in growth mechanism, i.e., vapor-liquid-solid (VLS) growth and vapor-solid (VS) growth. Photoluminescence spectra of the ZnO NWs exhibited a dominant near-band-edge (NBE) emission, indicating their high crystalline quality.

DOI： 10.1143/JJAP.44.L1410

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Multiwalled carbon nanotube (MWNT) films were grown on nickel-coated SiO2/Si substrates by atmospheric pressure chemical vapor deposition (CVD) using ethanol and nitrogen as a source material and a carrier gas, respectively. It is revealed that the ln(2)O(3):Sn (ITO)-coated glass placed in the reaction zone contributes to the enhancement of the carbon yield, the reduction of carbonaceous particles and the growth direction change of MWNTs. These effects are related to the suppression of the coalescence among the catalytic particles and the vaporization of the volatile compounds formed by the additional In, Sri and O elements evaporated from the ITO film.

DOI： 10.1143/JJAP.43.L1365

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Photoluminescence (PL) related to rare-earth (RE) impurities (Ho, Er and Eu) in AgGaS2 and CuGaS2 crystals has been studied. In Ho-doped AgGaS2 and CuGaS2, two series of PL lines are observed in 1.86-1.92 eV region and 2.24 eV region, and they are assigned to F-5(3)-I-5(7) and S-5(2)-I-5(8) transitions of the Ho3+ ion, respectively. Similarly, in Er-doped AgGaS2 and CuGaS2, Er3+-related two PL series are observed: 1.83-1.88 eV region (F-4(9/2)-I-4(15/2)) and 2.22-2.26 eV region (S-4(3/2)-I-4(15/2)). For both Ho and Er impurities, the profile of the PL spectrum in AgGaS2 is complex, and PL exhibited large number of lines compared with that in CuGaS2. The differences in PL spectra between this two compounds are related to the crystal field at the cation site and the local atomic arrangement of the RE impurities. This work also refers to the PL band at 2.28 eV observed for the Eu-doped AgGaS2 crystal. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(03)00246-4

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Highly c-axis oriented polycrystalline MgxZn1-xO (x < 0.20) thin films were prepared by chemical spray pyrolysis. It is found that the optical gap energy of the zinc oxide (ZnO) films is affected not only by the Burstein-Moss band-filling effect, but also by the bandgap narrowing effects such as electron-electron and electron-impurity interactions. The influence of the highly introduced donors and free-electrons is also confirmed on photoluminescence spectra of ZnO films via the broadening of the bound exciton line and the appearance of the non-k-conserving band-to-band emission. The MgxZn1-xO (x < 0.20) films exhibited a broad unstructured near-band-edge (NBE) emission shifting continuously towards higher energy side with increasing composition x. The NBE emission is ascribed to radiative transitions from tail states of the conduction band to those of the valence band. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(02)00736-8

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Metalorganic molecular beam epitaxy (MOMBE) growth of ZnO was carried out on the c-plane of sapphire substrate using diethylzinc (DEZn) and H2O as source precursors. ZnO layers were grown at substrate temperatures (T-s) between 200degreesC and 550degreesC. The c-axis oriented epitaxial ZnO layers were grown at T-s between 375degreesC and 400degreesC. Photoluminescence (PL) spectra at 8 K exhibited the neutral donor bound exciton peak at 3.36 eV. The PL intensity was maximum and the half-width was minimum (7 meV) for T-s of about 400degreesC. These results showed the quality of the ZnO layer grown by this MOMBE systerm was best at T-s of about 400degreesC. (C) 2002 Elsevier science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(01)01955-8

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Metalorganic molecular beam epitaxy (MOMBE) growth of ZnO was carried out on the c-plane of sapphire substrate using diethylzinc (DEZn) and H2O as source precursors. ZnO layers were grown at substrate temperature (Ts) between 200°C and 550°C. The c-axis oriented epitaxial ZnO layers were grown at Ts between 375°C and 400°C. Photoluminescence (PL) spectra at 8 K exhibited the neutral donor bound exciton peak at 3.36 eV. The PL intensity was maximum and the half-width was minimum (7 me V) for Ts of about 400°C. These results showed that the quality of the ZnO layer grown by this MOMBE system was best at Ts of about 400°C. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(01)01955-8

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Doping of Ho into AgGaS2 has been carried out by the thermal diffusion of Ho element into the undoped crystal. Sharp photoluminescence (PL) lines related to the S-5(2) --> 5I(8) and F-5(3) --> I-5(7) transitions in the Ho3+ ion are observed in the energy regions 2.23-2.28 and 1.85-1.93eV, respectively. Temperature dependence and excitation wavelength dependence of the PL indicate the existence of at least four types of He-related luminescence centers. Moreover, it is found that PL lines from different He-related luminescence centers exhibit different excitation and recombination mechanisms. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(99)00537-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Sharp photoluminescence (PL) lines related to the F-5(3)-> I-5(7) transitions in Ho3+ ion (1.85 similar to 1.93 eV) have been observed for single crystals of AgGaS2 doped with Ho prepared by thermal diffusion of Ho. The spectral shape of the series changed depending on the condition of thermal diffusion, suggesting the existence of several types of Ho-related luminescence centers. Moreover, it was found that the PL lines from the different luminescence centers exhibit different excitation and recombination mechanisms.

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Polycrystalline thin films of Cu-In-Se compounds and CuIn (SSei _42 alloys have been grown on glass substrate by chemical spray pyrolysis (CSP). Films are characterized by X-ray diffraction, optical absorption and Raman measurements. The Cu-In-Se films with In/(Cu+In) >0.57 exhibit a characteristic Raman peak. The optical bandgap energy of the Cu-In-Se film is approximately 1.22 eV for In/(Cu+In)<0.67, and it increases from 1.22 to 1.36 eV as the In/(Cu+In) ratio increases from 0.67 to 0.75. Controllability of alloy composition of CuIn(SSei_r)2 films is also discussed.

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Decay properties of sharp zero-phonon photoluminescence (PL) lines at 2.460 eV, 2.457 eV, 2.417 eV, 2.404 eV, 2.397 eV and 2.295 eV have been studied for CuGaS2 single crystals grown by an iodine transport method. These PL lines exhibited biexponential decay. The relationship between the decay time of the fast component (tau(f)) and the exciton localization energy (E-loc) can be given by tau(f) alpha E-loc(1.25). On the other hand, the decay times of the slow components (tau(s)) have been classified into two groups having different trends tau(s) alpha E-loc(2.7) and E-loc(0.5).

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Photoluminsecence (PL) studies have been carried out on the sharp zero-phonon lines at 2.461eV (H), 2.458eV (H'), 2.417 eV (R), 2.404 eV (S-0), 2.397eV (Q(0)) and 2.295 eV (T-0) in CuGaS2. The R, S-0, and Q(0) lines are enhanced by the thermal diffusion of Cu. The depth intensity profile showed that these sharp PL lines are related to defects created by the deviation from stoichiometry. Under high magnetic field (7T), the H line splits into three lines and the S-0 and R lines split into two lines. No splitting was observed for Q(0) and T-0 lines and also for the bound exciton lines (2.495, 2.493, 2.490 and 2.487 eV). These Zeeman results are discussed in terms of native defects and impurities included in the luminescence centers.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Epitaxial layers of CuGaSe2 and CuAlSe2 have been grown on the GaAs(100) substrate by means of molecular beam epitaxy (MBE) for the purpose of the preparation of hetero- and quantum structures. The c-axis oriented epilayers have been grown and the layers were characterized by photoluminescence (PL) and photoreflectance. The double heterostructures, CuAlSe2/CuGaSe2/CuAlSe2, with various well layer thicknesses (G) have been prepared. The PL measurement showed that the Cu(AlGai)Se-2 alloy is formed at the CuAlSe2/CuGaSe2 interface. The feasibility of preparation of the quantum structure using the CuAlSe2/CuGaSe2 system is discussed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

New photoluminescence from CuGaS2 appeared at the lower energy side of the free exciton luminescence under high excitation. The time-resolved spectrum of this luminescence at 0-20 ps after the excitation fits quite well with the calculated spectrum of the luminescence from the biexciton with the binding energy of 4.5 +/- 05 meV. Its time-integrated luminescence intensity was proportional to the excitation intensity to the power of similar to 2. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-1098(00)00035-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Excitation intensity dependences of time-integrated and picosecond time-resolved excitonic photoluminescence from CuGaS2 bulk single crystals were studied. Under high excitation broad and fast decay luminescence appeared at the lower energy side of free exciton luminescence. The new luminescence is attributed to the radiative recombination of biexcitons. The shape of the time-resolved spectrum of this luminescence at 0-20 ps after excitation fits quite well with "reverse" Boltzmann distribution for the biexciton temperature of similar to 54 K at the excitation level of 42 MW/cm(2) and binding energy of the biexciton of 4.5 +/- 0.5 meV. This is, to the best of our knowledge, the first observation of biexciton luminescence in CuGaS2.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Epitaxial layers of CuGaSe2, CuAlSe2 and CuInSe2 have been successfully grown on the GaAs(100) substrate by means of metalorganic molecular beam epitaxy (MOMBE). Cyclopentadienylcoppertriethylphosphine (Cp-CuTEP), triethygallium (TEGa), triisobuthylalminium (TIBA1), triethylindium (TEIn) and selenium have been used for precursors of Cu, Ga, Al, In and Se, respectively. Epilayers have been examined by X-ray diffraction, scanning electron microscopy, electron-probe micro analysis, Raman spectroscopy, photoluminescence and photoreflectance. The c-axis -oriented epilayers exhibiting good optical properties have been grown for both CuGaSe2 and CuInSe2. In spite of the poor reproducibility of the MOMBE growth of CuAlSe2, the epitaxial layer exhibiting the edge-emission at 2.64 eV at 8 K has been grown.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Photoacoustic (PA) spectra of CuInSe2 thin films prepared by chemical spray pyrolysis have been measured and compared with the Raman and X-ray diffraction results. Stoichiometric films having a sphalerite structure exhibit a PA band at similar to 0.95 eV, which is considered to be due to the electronic transition from copper atom substituting indium site (Cu-In) acceptor to indium atom substituting copper site (In-Cu) donor. In-rich films having the chalcopyrite structure with the In2Se3 second phase exhibit PA bands at similar to 0.90 eV and similar to 0.83 eV. The former PA band is considered to be due to the electronic transition from copper vacancy (V-Cu) acceptor to indium atom substituting selenium sire (In-Se) donor. The latter PA band is considered to be related to the defect complex involving In-Cu. For Cu-rich films, a PA signal below the absorption edge increases with increasing Cu/In ratio. This behavior is attributed to the increase in the content of the Cu-Se compound.

DOI： 10.1143/JJAP.38.4656

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Photoacoustic (PA) spectra of CuInSe2 thin films prepared by chemical spray pyrolysis have been measured and compared with the Raman and X-ray diffraction results. Stoichiometric films having a sphalerite structure exhibit a PA band at similar to 0.95 eV, which is considered to be due to the electronic transition from copper atom substituting indium site (Cu-In) acceptor to indium atom substituting copper site (In-Cu) donor. In-rich films having the chalcopyrite structure with the In2Se3 second phase exhibit PA bands at similar to 0.90 eV and similar to 0.83 eV. The former PA band is considered to be due to the electronic transition from copper vacancy (V-Cu) acceptor to indium atom substituting selenium sire (In-Se) donor. The latter PA band is considered to be related to the defect complex involving In-Cu. For Cu-rich films, a PA signal below the absorption edge increases with increasing Cu/In ratio. This behavior is attributed to the increase in the content of the Cu-Se compound.

DOI： 10.1143/JJAP.38.4656

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Time-resolved photoluminescence (PL) measurements have been carried out for CuGaS2 single crystals with a slightly Cu-rich composition grown by an iodine transport method. PL lines at 2.460 eV, 2.457 eV, 2.417 eV, 2.404 eV, 2.397 eV and 2.295 eV exhibited biexponential decay. The relationship between the decay time of the fast component (tau(f)) and the localization energy (E-loc) can be given by tau(f) proportional to E-loc(1.25). On the other hand, the decay times of the slow components (tau(s)) have been classified into two groups having different trends tau(s) proportional to E-loc(2.7) and E-loc(0.5). The difference between the two groups is discussed in terms of native defects and the iodine impurity included in the luminescence centers.

DOI： 10.1143/jjap.38.L805

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Language：English   Publisher：The Japan Society of Applied Physics  

Time-resolved photoluminescence (PL) measurements have been carried out for CuGaS2 single crystals with a slightly Cu-rich composition grown by an iodine transport method. PL lines at 2.460 eV, 2.457 eV, 2.417 eV, 2.404 eV, 2.397 eV and 2.295 eV exhibited biexponential decay. The relationship between the decay time of the fast component (τf) and the localization energy (Eloc) can be given by τf∝Eloc 1.25. On the other hand, the decay times of the slow components (τs) have been classified into two groups having different trends τs∝Eloc 2.7 and Eloc 0.5. The difference between the two groups is discussed in terms of native defects and the iodine impurity included in the luminescence centers.

DOI： 10.1143/jjap.38.L805

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The metalorganic molecular beam epitaxial growth of CuInSe2 layers on a GaAs(100) substrate was performed at (550 degrees C using cyclopentadienylcoppertriethylphosphine (CpCuTEP), triethylindium and selenium as source precursors. CuInSe2 layers with a flat surface were successfully grown. The epilayers were examined by X-ray diffraction, photoluminescence (PL) and photoreflectance measurements. The CuInSe2 layer grown under optimum conditions exhibited an exciton emission in the PL spectrum.

DOI： 10.1143/jjap.37.L1033

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The metalorganic molecular beam epitaxial growth of CuInSe2 layers on a GaAs(100) substrate was performed at (550 degrees C using cyclopentadienylcoppertriethylphosphine (CpCuTEP), triethylindium and selenium as source precursors. CuInSe2 layers with a flat surface were successfully grown. The epilayers were examined by X-ray diffraction, photoluminescence (PL) and photoreflectance measurements. The CuInSe2 layer grown under optimum conditions exhibited an exciton emission in the PL spectrum.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Thin films of CuGaS2 oriented toward c-axis have been grown on (100)GaP substrates using CuCl, diethylgalliumchloride and H2S by vapor phase epitaxy under simultaneous and alternate source feeding conditions. The films grown under completely separated alternate source feeding condition suggest atomic layer epitaxial growth of the compound, though data are not conclusive. The supply of H2S between two kinds of metal source supplies seems essential for this growth.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

CuGaS2 crystals grown from different starting materials by the iodine transport method showed different bound exciton luminescence lines, and total of 5 bound exciton (BE) lines were observed. Two of them were seen in absorption as well. From the absorption, concentrations of BE trapping centers were estimated to be of the order of 10(16)cm(-3). The sharp line at 2.4997 eV is supposed to be due to excitons bound to interstitials. The lines at 2.4909, 2.4934 and 2.4942 eV were found to have lifetimes of similar to 150 ps.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

First- and second-order Raman scattering and two-phonon infrared (IR) transmission measurement results for Cu(AlxGa1-x)S-2 single crystals have been examined as a function of x. It is apparent that the highest frequency B-2 and E modes at the zone center exhibit two-mode(persistence)-type behavior. The appearance of the two-mode-type behavior in a ternary alloy system is shown to be explainable by theoretical consideration based on a modified model of the type judging criterion. In addition, some of title two-phonon IR absorption bands and second-order Raman peaks are found to be due to phonons located at zone-boundary points. Compositional dependence of the A(1)(W-1) mode Raman line shape and the appearance of a cross-coupled phonon between the two modes indicate that the clustering effect is essentially suppressed in this alloy system.

DOI： 10.1143/JJAP.36.997

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

First- and second-order Raman scattering and two-phonon infrared (IR) transmission measurement results for Cu(AlxGa1-x)S-2 single crystals have been examined as a function of x. It is apparent that the highest frequency B-2 and E modes at the zone center exhibit two-mode(persistence)-type behavior. The appearance of the two-mode-type behavior in a ternary alloy system is shown to be explainable by theoretical consideration based on a modified model of the type judging criterion. In addition, some of title two-phonon IR absorption bands and second-order Raman peaks are found to be due to phonons located at zone-boundary points. Compositional dependence of the A(1)(W-1) mode Raman line shape and the appearance of a cross-coupled phonon between the two modes indicate that the clustering effect is essentially suppressed in this alloy system.

DOI： 10.1143/JJAP.36.997

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have measured the first-order Raman spectra of CuAlSe2 and the second-order Raman spectra of CuAlS2 and CuAlSe2, and reexamined two-phonon absorption spectra of CuAlS2. Lattice dynamical calculations have been performed using a rigid ion model. Force constants and charges as fitting parameters have been determined so as to reproduce zone-center phonon frequencies and the two-phonon spectra observed, Calculated two-phonon density of states shows reasonable agreements with those spectra.

DOI： 10.1016/0921-4526(95)00790-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have measured the first-order Raman spectra of CuAlSe2 and the second-order Raman spectra of CuAlS2 and CuAlSe2, and reexamined two-phonon absorption spectra of CuAlS2. Lattice dynamical calculations have been performed using a rigid ion model. Force constants and charges as fitting parameters have been determined so as to reproduce zone-center phonon frequencies and the two-phonon spectra observed, Calculated two-phonon density of states shows reasonable agreements with those spectra.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

In the alternate feeding of metal chlorides (CuCl, GaCl3) and H2S sources, the growth rate saturation of CuGaS2 on GaP was observed for substrate temperatures between 530-degrees-C and 570-degrees-C, and also for some range of H2S flow rate. Together with the growth rate saturation behavior for metal chlorides reported in our previous paper, these results can be considered to indicate achievement of atomic layer epitaxy (ALE) of CuGaS2. The growth orientation change leading to c-axis growth was observed for a large H2S flow rate. Some possibility of stoichiometry control by ALE was suggested from photoluminescence spectra.

DOI： 10.1143/jjap.33.L244

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The broad emission bands appearing at 6700 angstrom, 7500 angstrom and 8600 angstrom were discussed in terms of preparation processes of epitaxial films and bulk crystals. For the emission at 7500 angstrom showing spectral shifts during decay, characteristic to donor-acceptor-pair type recombinations, possible relation is pointed out to sulfur vacancies and interstitial halogen (Cl or 1) atoms in films or bulk crystals.

DOI： 10.7567/JJAPS.32S3.618

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The broad emission bands appearing at 6700 angstrom, 7500 angstrom and 8600 angstrom were discussed in terms of preparation processes of epitaxial films and bulk crystals. For the emission at 7500 angstrom showing spectral shifts during decay, characteristic to donor-acceptor-pair type recombinations, possible relation is pointed out to sulfur vacancies and interstitial halogen (Cl or 1) atoms in films or bulk crystals.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Investigations were made on band-edge-region photoluminescence and the electric resistivity of CuGaS2 epitaxial films on GaAs and GaP substrates, which were prepared by vapor phase epitaxy using metal chlorides and H2S gas. The similar temperature dependence was observed on the resistivity and the intensity of 2.40 eV emission, giving nearly the same activation energy of about 0.05 eV. This value suggests the existence of an acceptor shallower than the acceptor of effective mass approximation. A proposed candidate of this shallow acceptor is an interstitial chlorine atom coming from source materials.

DOI： 10.7567/JJAPS.32S3.621

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Investigations were made on band-edge-region photoluminescence and the electric resistivity of CuGaS2 epitaxial films on GaAs and GaP substrates, which were prepared by vapor phase epitaxy using metal chlorides and H2S gas. The similar temperature dependence was observed on the resistivity and the intensity of 2.40 eV emission, giving nearly the same activation energy of about 0.05 eV. This value suggests the existence of an acceptor shallower than the acceptor of effective mass approximation. A proposed candidate of this shallow acceptor is an interstitial chlorine atom coming from source materials.

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

Heterostructures of CuO/ZnO synthesized on the Au seed layers from the aqueous solution of ZnCl_2 and that of CuCl showed aggregates of CuO nanorods (NRs) covering the volcano-like ZnO NRs. Both the CuO/ZnO superstrate and ZnO/CuO substrate structures synthesized from the aqueous solution of Zn(CH_3COO)_22H_2O and that of Cu(NO_3)_22H_2O exhibited smooth interfaces. Especially, the latter showed a rectifying behavior on its current-votage characteristic.

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Structural and optical properties of polycrystalline In-rich Cu-In-Se (0.55<In/(Cu+In)<0.85) and MgxZn1-xO (x<0.20) films prepared by chemical spray pyrolysis (CSP) were investigated. Raman spectra of In-rich Cu-In-Se films exhibited a characteristic Raman peak shifting to the lower frequency side as the In/(Cu+In) ratio increased, which can be utilized for the study of structural disordering. For the ZnO films, the optical gap energy (Eg,opt) and the photoluminescence (PL) peak energy of the near-band-edge (NBE) emission shifted to the high energy side with increasing substrate temperature (TS), suggesting the shift is due to the Burstein-Moss effect. The successful growth of the MgxZn1-xO films (x<0.20) has been achieved. A dominant. NBE emission and Eg,opt exhibited the blue shift with increasing alloy composition x.

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DOI： 10.11470/oubutsu1932.64.137

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