No.1 別紙第１号様式 was also been discussed. (1) The crystal quality and the thickness of films deposited at 600 oC increase with the 博 専攻名 氏 士 論 文 の 要 increasing of oxygen pressure. The growth mode of the 旨 films is island mode. (2) By varying the substrate システム創成科学専攻 名（本籍） 張 法碧（中国） 印 temperature, the evolutions of the structure, surface 博士論文題名 morphology and bandgap have been clearly clarified. Growth and characterization of Ga2O3 based wide Films deposited at substrate temperature below 400 oC bandgap semiconductor films show amorphous structure while those deposited at （酸化ガリウム系ワイドギャップ半導体薄膜の substrate temperature higher than 500 oC are of high 作製と評価） oriented monoclinic structure. (3) The optimized growth substrate temperature and oxygen pressure for our experiment is 500 oC and 0.1 Pa. The growth relationship 要旨 have between the film and the substrate is: sapphire (0001) // become the hot spot of recent research for the possible β-Ga2O3 (-201) and sapphire [11-20] // β-Ga2O3 [102]. using in many fields such as light emitting devices, The obtained β-Ga2O3 film is of sixfold in-plane power devices and flame detectors. Among all the wide rotational symmetry. The hard X-ray photoemission bandgap materials, β-Ga2O3 film with the monoclinic spectroscopy reveals that the valence band of the structure is considered as a promising candidate for its crystalline films is mainly due to the hybridization of Ga large bandgap and chemical and physical stabilities. And 4sp. (4) By varying the growth time (film thickness), the it is also suitable for extreme environment applications growth process has been investigated. (5) Post annealing such as high temperatures, intense radiation and (annealing temperature from 700 to 900 oC) cannot be corrosive environments. However, the bandgap should used to obtain films with better crystal quality than the be tuned to realize high sensitive wavelength tunable film deposited under the optimized growth conditions. photodetectors, cutoff wavelength-tunable optical filters The films with post annealing show smaller blue/UV or to introduce shallow impurity levels for good emission ratio. Wide bandgap semiconductor materials electronic properties. In Chapter 4, we have investigated the Si doping In Chapter 1, the background including the influence on the structure and properties of Ga2O3 films. properties and the review of studies on Ga2O3, (1) Ga2O3 films with different Si content were grown on (Ga1-xInx)2O3, (AlxGa1-x)2O3 and Si doped Ga2O3 were sapphire substrate at 500 oC by PLD. All of the films described. The purpose or the motivation of this study exhibit smooth surfaces and high transmittances. The was presented. films of Si content lower than 4.1 at. % show high (-201) In Chapter 2, the film growth and characterization methods were introduced. oriented monoclinic structure. The carrier density of Ga2O3 film has been increased to 9.1×1019 cm-3 with In Chapter 3, we have investigated the influences of conductivity of 2.0 S cm-1 by 1.1 at. % Si doping. Further oxygen pressure, substrate temperature and deposition increase of Si content leads to the decrease of carrier time on the structure and optical properties of Ga2O3 density. (2) By varing the substrate temperature, it is films grown by PLD. The influence of post annealing found that film deposited at 500 oC (1 wt.% Si doped) No.2 別紙第１号様式 under different gas ambients (N2, vacuum, Ar, O2) or at different temperatures (700~1000 oC). It is found that gas 博 専攻名 氏 士 論 文 の 要 旨 システム創成科学専攻 名（本籍） 張 法碧（中国） ambient and temperature have important influence on crystal quality of annealed (GaIn)2O3 films. Only oxygen ambient can crystallize (GaIn)2O3 film and film annealed in shows lowest conductivity and highest carrier density while possesses best crystallinity. (3) Oxygen pressure has no obviously influence on the electrical properties of Si-doped Ga2O3, indicating the oxygen deficiency is not the main origin of the conductive carrier in our study. In Chapter 5, we showed the growth of crystalline and bandgap tunable (Ga1-xInx)2O3 films on sapphire (0001) substrate. The elimination of the phase separation was discussed in detail. (1) Optical analysis indicates that the bandgap of the (GaIn)2O3 films grown by PLD can be tailored from 3.8 eV to 5.1 eV by controlling the In content. Single phase (GaIn)2O3 films were obtained although films with nominal In content between 0.2 and 0.5 exhibit phases separation. (2) (GaIn)2O3 films with nominal In content of 0.3 were deposited on sapphire substrate by PLD at substrate temperatures from RT to 500 oC. The phase separation were observed for the films grown at substrate temperature higher than 300 oC while the films grown at substrate temperature lower than 200 o C revealed homogenous element distributions with amorphous structures. Thermal annealing had no obvious effects on films grown at substrate temperature higher than 300 oC. The clusters remained on the surface of the films after thermal annealing treatment. On the other hand, however, by thermal annealing the film deposited at RT in atmosphere, (GaIn)2O3 film with smooth surface, homogenous element distribution, high orientation crystal and high optical transmittance was successfully obtained. (3) In order to understand the annealing effects, (GaIn)2O3 films with nominal In content of 0.3 as-deposited in room temperature have been annealed 800 o C appears best crystal quality. X-ray photoelectron spectroscopy analysis indicated that oxygen ambient annealing has greatly helped on decreasing the oxygen vacancy. (4) (GaIn)2O3 films with different nominal In contents from 0.2 to 0.7 annealed at 800 oC under O2 ambient also showed high crystal quality, improved optical transmittance, and smooth surface. Thus, high oriented films with nominal In content from 0.2 to 0.7 without phase separation can be obtained through annealing process. Complementally, high oriented films without phase separation can be obtained in the nominal indium content regions of 0 to 0.1 and 0.9 to 1.0 for the film deposited at 500 oC. By combing the two processes, bandgap tunable high quality (GaIn)2O3 films throughout the whole indium content range from 0 to 1 can be successfully obtained. In Chapter 6, bandgap tunable (AlGa)2O3 films were deposited on sapphire substrates by PLD. The deposited films are of high transmittance as measured by spectrophotometer. The Al contents in films increase linearly with that of the targets. The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of (AlGa)2O3 films as it is in good agreement with the bandgap values from transmittance spectra. The measured bandgap of (AlGa)2O3 films increases continuously with the Al content covering the whole Al content range from about 5 to 7 eV, indicating PLD is a promising growth technology for growing bandgap tunable (AlGa)2O3 film.
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