Toshihiro Miyata

Highly transparent and conductive rare earth-doped ZnO thin films prepared by magnetron sputtering

Abstract Highly transparent and conductive thin films of ZnO doped with a rare-earth element, Sc or Y, have been prepared by d.c. magnetron sputtering using a powder target. The resistivity of the ZnO:Sc thin films was always lower than that of the ZnO:Y thin films; a resistivity in the order of 10 −4 Ω cm was obtained in these films. The resistivity of the ZnO:Sc thin films decreased as the Sc 2 O 3 content was increased up to about 2 wt.%; any further increase of the Sc 2 O 3 content caused the resistivity to increase. A resistivity of 3.1 A×10 −4 Ω cm was obtained in ZnO:Sc thin films prepared on a glass substrate at a temperature of 200°C with a Sc 2 O 3 content of 2 wt.%. An average transmittance of above 85% in the visible range was obtained for doped ZnO thin films. The electrical and optical properties, as well as the thermal stability of resistivity, of the ZnO:Sc thin films were comparable to those of ZnO:Al.

Work function of transparent conducting multicomponent oxide thin films prepared by magnetron sputtering

Abstract The work function of transparent conducting multicomponent oxide (TCO) films is reported. TCO films consisting of binary oxides, such as In 2 O 3 , SnO 2 and ZnO, and ternary oxides, such as Zn 2 In 2 O 5 , In 4 Sn 3 O 12 , GaInO 3 , ZnSnO 3 and MgIn 2 O 4 , were prepared by magnetron sputtering. In addition, transparent conducting films consisting of multicomponent oxides composed of combinations of these binary or ternary oxides were also prepared by magnetron sputtering. The work function of these TCO films was measured by ultraviolet photoelectron spectroscopy operated in air. It was found that the work function as well as the electrical, optical and chemical properties of transparent conducting multicomponent oxide films could be controlled by varying the chemical composition.

High-Efficiency Oxide Solar Cells with ZnO/Cu2O Heterojunction Fabricated on Thermally Oxidized Cu2O Sheets

High conversion efficiencies were achieved in low cost n–p heterojunction oxide solar cells with an Al-doped ZnO (AZO)/non-doped ZnO (ZO)/Cu2O structure. This achievement was made possible by the formation of an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu2O sheets produced by the thermal oxidization of copper sheets: n-ZO thin film optimal thickness ranges from 30 to 50 nm. Photovoltaic characteristics such as an open circuit voltage of 0.69 V, a fill factor of 0.55 and a conversion efficiency of 3.83% were attained under simulated AM1.5G solar illumination.

High-Efficiency Cu2O-Based Heterojunction Solar Cells Fabricated Using a Ga2O3 Thin Film as N-Type Layer

High-efficiency heterojunction solar cells consisting of a nondoped Ga2O3 thin film as an n-type semiconductor layer and a p-type Cu2O sheet as the active layer as well as the substrate, prepared by thermally oxidizing a Cu sheet, are demonstrated. The use of an n-type Ga2O3 thin film can greatly improve the performance of n-Ga2O3/p-Cu2O heterojunction solar cells. The highest efficiency of 5.38% was obtained in an Al-doped ZnO/Ga2O3/Cu2O heterojunction solar cell fabricated with an n-Ga2O3 thin-film layer prepared at room temperature with a thickness of 75 nm by a pulsed laser deposition method.

Transparent conducting impurity-co-doped ZnO:Al thin films prepared by magnetron sputtering

This report describes the effects of impurity-co-doping on transparent conducting Al-doped ZnO (AZO) films prepared by DC magnetron sputtering using a target composed of dopant powder added to a mixture of ZnO and Al2O3 powder. The chemical stability of transparent conducting AZO films could be improved by co-doping Cr or Co without significantly altering the original electrical and optical properties. A reduction in etching rate, as well as a low resistivity of 3.0×10−4 Ω cm, was obtained in transparent conducting AZO:Cr films prepared using Zn powder added into the oxide target with an Al2O3 content of 2 wt.% and a Cr2O3 content of 1 wt.%. In addition, a reduction in etching rate, as well as low resistivity, was obtained in transparent conducting AZO:Co films prepared with an Al2O3 content of 2 wt.% and a CoO content of 0.5–2 wt.% or a CoCl2 content of 1.5–3 wt.%.

High rate deposition of transparent conducting oxide thin films by vacuum arc plasma evaporation

Transparent conducting oxide (TCO) thin films have been deposited at a high rate above 370 nm/min by vacuum arc plasma evaporation (VAPE) using sintered oxide fragments as the source material. It was found that the deposition rate of TCO films was strongly dependent on the deposition pressure, whereas the obtained electrical properties were relatively independent of the pressure. Resistivities of 5.6×10−4 and 2.3×10−4 Ω·cm and an average transmittance above 80% (with substrate included) in the visible range were obtained in Ga-doped ZnO (GZO) thin films deposited at 100 and 350 °C, respectively. In addition, a resistivity as low as 1.4×10−4 Ω·cm and an average transmittance above 80% were also obtained in indium-tin-oxide (ITO) films deposited at 300 °C. The deposited TCO films exhibited uniform distributions of resistivity and thickness on large area substrates.

Heterojunction solar cell with 6% efficiency based on an n-type aluminum–gallium–oxide thin film and p-type sodium-doped Cu2O sheet

In this paper, we describe efforts to enhance the efficiency of Cu2O-based heterojunction solar cells fabricated with an aluminum–gallium–oxide (Al–Ga–O) thin film as the n-type layer and a p-type sodium (Na)-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing copper sheets. The optimal Al content [X; Al/(Ga + Al) atomic ratio] of an AlX–Ga1−X–O thin-film n-type layer was found to be approximately 2.5 at. %. The optimized resistivity was approximately 15 Ω cm for n-type AlX–Ga1−X–O/p-type Cu2O:Na heterojunction solar cells. A MgF2/AZO/Al0.025–Ga0.975–O/Cu2O:Na heterojunction solar cell with 6.1% efficiency was fabricated using a 60-nm-thick n-type oxide thin-film layer and a 0.2-mm-thick Cu2O:Na sheet with the optimized resistivity.

Gallium oxide as host material for multicolor emitting phosphors

Abstract Ga2O3 as the host material for multicolor-emitting phosphors, in particular, for thin-film electroluminescent (TFEL) devices has been described. High-luminance multicolor emissions were realized by TFEL devices with a Mn-, Cr-, Co-, Sn- or rare-earth-activated Ga2O3 phosphor.

Transparent conducting ZnO thin films prepared on low temperature substrates by chemical vapour deposition using Zn(C5H7O2)2

Abstract Transparent and conducting zinc oxide (ZnO) films have been prepared on glass substrates by atmospheric and low pressure chemical vapour deposition (CVD) using zinc acetylacetonate (Zn(C 5 H 7 O 2 ) 2 ) and various oxygen sources such as air, water (H 2 O) and hydrogen peroxide (H 2 O 2 ). A resistivity of (4–6) × 10 −3 Ω cm and an average transmittance above 80% in the visible range were obtained for undoped ZnO thin films prepared at a substrate temperature of 550°C using H 2 O or H 2 O 2 . It was found that H 2 O and H 2 O 2 , which include hydrogen, were better oxygen sources than an oxygen-containing gas such as air. The deposition rate of ZnO films was controlled by the Zn(C 5 H 7 O 2 ) 2 temperature. Al-doped ZnO films with a resistivity as low as 4.6 × 10 −3 Ω cm were prepared at a substrate temperature of 350°C by CVD at a low pressure of 60 Torr using aluminium acetylacetonate (Al(C 5 H 7 O 2 ) 3 ) as the dopant source.

Transparent conducting zinc-co-doped ITO films prepared by magnetron sputtering

Abstract Zn-co-doped indium-tin-oxide (ITO) films have been prepared by dc magnetron sputtering using powder targets. Zn-co-doped ITO films with a practical etching rate as well as a low resistivity were obtained; in particular, etching rate could be controlled by varying the Zn content doped into ITO. In addition, a resistivity of 2–3×10−4 Ω cm was obtained in Zn-co-doped ITO films prepared with a Sn content of 9.3 at.% and a Zn content of 0–34.1 at.% under optimized target preparation and sputter deposition conditions. The spatial distribution of electrical properties on the substrate surface in Zn-co-doped ITO films was considerably affected by the Zn content. A relatively uniform distribution of electrical properties was obtained in films prepared with a Zn content in the range of 15–34.1 at.%.