Minoru Oshima

Low-Temperature Growth of ZnO Films by Spray Pyrolysis

Nondoped ZnO film on a polyethylene terephthalate film was successfully grown by conventional spray pyrolysis at 100 °C using a diethylzinc-based solution under air atmosphere. The samples had an average optical transmittance of more than 80%, a flat surface, and an a-axis orientation from the optical transmittance, scanning electron microscopy, and X-ray diffraction measurements, respectively. It was assumed that the growth at low temperature was attributed to atmospheric oxygen and/or steam.

Structural and electrical characterization of AgInSe2 crystals grown by hot-press method

Undoped polycrystalline AgInSe2 crystals were successfully grown at low temperature (650°C) using a hot-press method. The sizes of the samples were 2 cm in diameter. The largest grain size was approximately 90 nm. The presence of lattice defects such as Ag interstitials might lead to an enhancement in n-type electrical conductivity. The crystals had a resistivity of 2.2 Ω cm, a carrier concentration of 4.2 × 1016 cm3 and a mobility of 70 cm2V-1s-1 obtained by Hall measurement at RT.

Growth and Annealing of ZnO Films Grown by Spray Pyrolysis

Undoped and In-doped ZnO films on glass substrate were successfully grown by spray pyrolysis at 500 °C. The samples were annealed under N2 atmosphere between 100 and 600 °C for 5 min. The lattice constants and grain sizes of both samples were unchanged with increasing annealing temperature. However, the photoluminescence intensity of the In-doped sample markedly decreased in comparison with that of the undoped sample with increasing annealing temperature. The carrier concentration increased with increasing annealing temperature. These findings indicated that the number of nonradiative recombination centers of the In-doped ZnO samples markedly increased.

Annealing effects of In-doped ZnO films grown by spray pyrolysis method

In-doped (2 mol%) ZnO films on glass substrate were grown by spray pyrolysis method at 500 °C. Samples were annealed under N2 atmosphere between 100 and 600 °C for 5 min. The X-ray diffraction spectra indicated that the c-axis intensity ratio for a-axis was slightly increased with increasing annealing temperature. This meant that a degree of crystalinity increased with increasing annealing temperature. However, photoluminescence intensity decreased with annealing temperature, indicating that the increased the number of nonradiative recombination centers in the In-doped ZnO films.

Low Sheet Resistivity of Transparent Ga-Doped ZnO Film Grown by Atmospheric Spray Pyrolysis

Ga-doped ZnO film on polyethylene terephthalate film was successfully grown at 150 °C by conventional atmospheric spray pyrolysis using diethylzinc-based solution. The samples had an average optical transmittance of more than 80% and were strongly a-axis orientated according to the result of optical transmittance and X-ray diffraction analyses, respectively. The n-type Ga-doped ZnO films had a low sheet resistivity of 250 Ω/ at an optimal Ga content of 1 at. % upon UV irradiation.

Characterization of Spin Coated Nondoped and In-Doped ZnO Films Using Novel Precursor Solution

A novel precursor for ZnO film deposition with Zn-O structure was synthesized by the reaction of diethylzinc and water in some ether solvents. The novel precursor was characterized by 1H-NMR spectroscopy and differential scanning calorimetry (DSC). Nondoped and In-doped ZnO films on a glass substrate have been successfully grown by conventional spin coating using nondoped and In added novel precursor solution. The samples have an optical transmittance of more than 85%, and a smooth surface determined from optical transmittance and scanning electron microscopy, respectively. The sheet resistivity of In-doped ZnO films is lower than that of nondoped ZnO film.

Characteristic of Low Resistivity Fluorine-Doped SnO2 Thin Films Grown by Spray Pyrolysis

Transparent conducting oxide films of fluorine-doped SnO2 (FTO) were deposited on glass substrates by spray pyrolysis in order to determine the effect of spray solution concentration. These films were prepared with different F-doping concentrations from 0 to 33 mol %. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol % at a substrate temperature of 500 °C. These conditions resulted in a film with an average transmittance of 82%, a resistivity of 4.0 ×10-4 Ω cm, a carrier concentration of 4.7 ×1020 cm-3 and a mobility of 34 cm2 V-1 s-1.

Electrical Properties of Fluorine Doped Tin Dioxide Film Grown by Spray Method

Low resistivity, fluorine-doped tin dioxide thin films were deposited on glass substrates by spray pyrolysis. These films were prepared with different F-doping concentrations from 0 to 33 mol%. The structure of these films was investigated by X-ray diffraction and the surface morphology by Scanning Electron Microscopy. Sample compositions were evaluated using X-ray Photoemission Spectroscopy. According to these results, the films were all polycrystalline with tetragonal crystal structures. Hall measurements were used to probe the dependence of the resistivity on temperature for un-doped SnO2 and F-doped SnO2. The resistivity of un-doped SnO2 slightly increased with increasing temperature. Conversely, the resistivity of F-doped SnO2 slightly decreased with increasing temperature.

Thickness Dependence of Structure and Optical Characteristics in Fluorine-Doped SnO2 Films Grown by Spray Pyrolysis Method

Transparent conducting thin films of fluorine-doped SnO2 were deposited on glass substrates by a spray pyrolysis technique in order to investigate the effect of film thickness. These films were prepared at a substrate temperature of 500 °C. The thickness of the samples was between approximately 70 nm and 1.5 µm. The preferred grain orientation of the films varied with increasing film thickness. The grain size of the surface increased with increasing film thickness. Crystal growth occurred at several stages of film growth. In the first stage, pores were formed in the film. Secondly, the grains grew in two dimensions and completely coved the substrate surface. Finally, the grains became columnar crystals with increasing film thickness. The electrical resistivity decreased with increasing film thickness although this was accompanied by a decrease in optical transmittance. The IR absorption increased despite a constant carrier concentration. Film thickness also increased. This result meant that with a constant high carrier concentration, the increased film thickness enhanced the absorption.

Structural and Electronic Structure of SnO2 by the First-Principle Study

We performed first-principle calculations to investigate the effects of F, Cl and Sb impurities on the electronic properties of SnO2. We obtained, firstly, the electronic structure of SnO2, a valence band maximum of SnO2 is an O 2p orbital and a conduction band minimum was an antibonding Sn 5s and O 2p orbitals dominantly. Secondly, those impurites doped SnO2 was obtained the electronic structure. The F, Cl and Sb impurities as n-type dopants exhibited shallow donors. This calculation results were in good agreement with our prvious experiment that we obtained the low resistivity SnO2.