| Gallium oxide, as a new type of wide bandgap semiconductor materials, with many excellent physical properties (such as: the wide bandgap, ?4.9 eV; the large breakdown electric field, ? 8 MV/cm),exhibits the wide device application prospect in field effect transistor,solar-blind photodetector, transparent conductive electrode, information storage, gas sensor, LED substrate and so on. In recent years, especially since the high quality 2 inch of gallium oxide single crystal was obtained,gallium oxide materials have attracted intensive attentions by researchers from all over the world. And it is forming the hot spot. The first International Workshop on Gallium Oxide and Related Materials 2015(IWGO 2015) had been held in November 2015, Kyoto university in Japan. During the period of my doctor, I'm in the forefront of academic and competing to drive ahead. Combined with the discipline characteristic of Beijing University of Posts and Telecommunications, I carried out the application research of gallium oxide thin film materials in photodetector, magnetic semiconductor memory and resistance change memory. The obtained results can be concluded as the following several aspects:(1). The influences of the different substrate, oxygen pressure,temperature, laser energy and frequency on the crystalline phase, crystal quality, the bandgap of gallium oxide thin film were studied by laser molecular beam epitaxy technology. Results show that it is easy to obtain along (201) preferential ?-Ga2O3 films for c plane sapphire substrate and easy to obtain along (300) preferential ?-Ga2O3 films for m plane sapphire substrate.The bandgap of ?-Ga2O3 and ?-Ga2O3 films were 4.90 and 5.15 eV. The optimal growth conditions for ?-Ga2O3 epitaxial thin film is oxygen pressure of 5×10-3 Pa and substrate temperature of 750?.(2). The metal-semiconductor-metal structure photodetector based on gallium oxide thin film was fabricated. The photodetector is very sensitive to the light of 254 nm and shows almost no response to the light of 365 nm, exhibiting the obvious solar-blind photoelectric properties.Realization of Ti/?-Ga2O3 interface changing from Ohmic type to the Schottky type to control the transportation of photogenerated carriers effectively by decreasing the oxygen vacancy concentration in ?-Ga2O3 thin films through annealing in oxygen atmosphere. What's more, it can effectively inhibit the unintentional extra carriers by the valence state transition of doping element Mn3+/Mn2+, which reduces the concentration of oxygen vacancy and the dark current of photodetector, improves the sensitivity and photoresponse time of photodetector.(3). We put forward a kind technique to achieve doping and control the microstructure of thin film through alternate depositing and interdiffusing the Ga2O3 and transition metal (Mn, Fe, Cr) ultra thin layers in high temperature. We obtained high concentration uniform doping along (201) preferential ? phase (GaMn)2O3 epitaxial thin film for Mn, Ga2O3/(Ga1-xFex)2O3 multilayer epitaxial thin film for Fe and Cr doped Ga2O3 nanoworm thin film for Cr. The room temperature ferromagnetism was observed in above three kinds structure thin film,and the origin of magnetism was given.(4). Since the resistance of gallium oxide is sensitive to oxygen, we reported unipolar resistance switching behavior and abnormal bipolar resistance switching behavior respectively based on gallium oxide thin films for the first time. Unipolar resistance switching behavior has a good repeatability and stability. The low resistance state shows metal behavior.And the high resistance state exhibits semiconductor behavior. The observed unipolar resistance switching behavior can be explained by the formation/rupture of conductive filaments formed out of oxygen vacancies. Abnormal bipolar resistance switching behavior also shows a high stability, and free conversion between high and low resistance state.The low resistance state shows electron tunneling. And the high resistance state exhibits a conduction of Schottky-type. The observed abnormal bipolar resistance switching behavior is considered to be related to the migration of oxygen vacancies which changes the space charge region width of the metal/semiconductor interface and results in a different electron transport mechanism. |
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