| β-Ga2O3is regarded as a promising candidate material for optoelectronic devices because of its wide direct bandgap of4.2-4.9eV.β-Ga2O3has stable structure properties and stable optoelectronic properties, meanwhile, the transmissivity of β-Ga2O3is high in near ultraviolet, visible light and near infrared light region. At room temperature, crystal β-Ga2O3exhibits n type conducting properties due to the gallium vacancies and oxide vacancies. Doping with other element, such as Si、Sn and so on, would improved the conducting properties of β-Ga2O3material. As reported, doping with Dy, Eu and N element, would change the optical properties of β-Ga2O3. β-Ga2O3is regarded as the novel and promising candidate for ultraviolet photodectors. The β-Ga2O3films have been prepared by several methods, such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and sputtering. However, there are few reports on the thermal evaporation technique. As is well known, the thermal evaporation technique is traditional and convenient method to fabricate film. Herein, it is flexibly and widely employed in industrial manufacture with the advantage of fast depositing rate. Ploy crystalline semiconductor material has unique properties comparing with crystalline material. It is easy to prepared polycrystalline β-Ga2O3. It is focusing much attention on the polycrystalline β-Ga2O3because of some excellent properties. In this paper, using electron beam evaporation method, we prepared β-Ga2O3and Cu doped β-Ga2O3film on sapphire and silicon substrate, respectively. The detailed work is shown as following.Using electron beam evaporation method, β-Ga2O3was deposited on c-plane Al2O3substrates. As-grown β-Ga2O3samples were subsequently annealed at1000℃under nitrogen or oxygen for1hour. And the micorstructure, surface morphology and optical properties were investigated. It was indicated that the annealing treatment in oxygen atmosphere was more effective to improve the crystalline properties of β-Ga2O3than in the nitrogen atmosphere. The photoluminescence (PL) showed broad ultraviolet emission centered at330nm and broad red emission centered at706nm. The optical bandgap of β-Ga2O3was deduced to be5.1and5.7eV, which was distinctly different with that’s of the bulk crystal. Based on the X-ray diffraction (XRD), surface morphology and selected area transmission electron microscope images, It was suggested the quantum size effect caused the broadening of the optical bandgap. Fourier transforming infrared (FTIR) transmittance spectra was recorded in the range of3600-400cm-1. The IR band at460cm-1was assigned to Ga-O vibrations, and the band at670cm-1was relative with the β-Ga2O3. The band at760cm-1was assigned to Ga-OH vibrations. In addition, the new band at560cm-1was deduced to be arising from the β-Ga2O3.Particularly for special application, the β-Ga2O3was evaluated to be the excellent sacrificial substances in the GaN/Ga2O3/sapphire structure. As is well known, the thermal conductivity of sapphire is not high enough for large scale GaN based light emitting diodes (LED). One of effective ways of enhancing the performance of optoelectronic devices is the transfer of prefabricated devices from conventional sapphire substrates onto more thermally and electrically conductive substrates. Due to the2.6%of the minimum lattice mismatch between β-Ga2O3and GaN, the successful growth of GaN on Ga2O3buffer layers has been reported to act as the sacrificial materials for chemical lift off process. Generally, epitaxial growth of GaN on sapphire with MOCVD method required high temperature around1000℃. Both sacrificial buffer layers and various optoelectronic devices based on Ga2O3material required stable and reliable structural and physical properties, especially in the conditions of active oxygen ambient at high temperature. β-Ga2O3films with polycrystalline structure were prepared on c-plane sapphire substrate. XRD patterns indicated that the grain orientations were promoted and the grain sizes enlarged with annealing time increasing. Considered the XRD patterns, the Ga2O3films annealed for30,60and90minutes showed similar structure properties. The PL spectra exhibited violet, green and red emissions, which were affected by the annealing time. Therefore, it was concluded that the β-Ga2O3films would remain stable structure and optical characteristics when they were annealed for30to90minutes. However, if the annealing treatment time arrived to120minutes, the crystalline properties of β-Ga2O3film became worse.Cu doped β-Ga2O3thin films were deposited by electron beam method with subsequent annealing at1000℃for1hour. The influence of the Cu dopant on the crystal structure, surface morphologies and optical properties of β-Ga2O3films was investigated. XRD patterns indicated that the optimum orientations of the films were promoted by high temperature annealing treatment. The PL spectra of the annealed samples presented violet and green emissions, and the peak of green emissions red shift to520nm wavelength. The X-ray photoelectron spectroscopy (XPS) result indicated that the Cu ions were effectively doped into the β-Ga2O3films with univalent and bivalent chemical states. Then, we researched the effects of the deposit parameters on the Cu doped β-Ga2O3thin films properties, such as annealing temperature, substrate growth temperature and depositing speed. In summaries, we obtained the optimized deposit parameter of Cu doped β-Ga2O3films, which was400℃of substrate temperature and1000℃of annealing temperature. It would be useful to future research on the properties of Cu doped β-Ga2O3films.Lastly, we prepared the β-Ga2O3film and Cu doped β-Ga2O3films on silicion substrate. The influence of the silicon substrate on the crystal structure and optical properties of β-Ga2O3films was investigated by X-ray diffraction, photoluminescence spectra and FTIR transmittance spectra. |
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