Development Of Gallium Oxide Thin Films Solar-blind Ultraviolet Photoconductors

In recent years, the solar-blind ultraviolet detecting technology is widely concerned because its advantages of strong anti-interference ability and high sensitivity. While the solar-blind ultraviolet detectors based on wide band gap semiconductor has gradually replace the vacuum phototube become the mainstream of the current research direction because its advantages of small size, long life and low power consumption. Compared with Al Ga N, Zn Mg O and other common solar-blind ultraviolet sensitive material, β-Ga2O3 has a large band gap and can be easier to fabricate high-quality films, is a very suitable material for solar-blind ultraviolet detector. In this thesis, solar-blind ultraviolet photoconductors were fabricated based on the β-Ga2O3 thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy. in order to improve the device performance, Many approaches have been tried to improve the quality of β-Ga2O3, On this basis, In order to realize miniaturization of the device, lay the foundation for the later development of large area solar blind ultraviolet detector array,the scaling characteristics of the device have been discussed to study the effect of device size on device performance,and a diode assisted photoconductor has been studied. The concrete contents include following points:（1） Explore the effects of annealing on photoelectric properties of β-Ga2O3 Thin Films. In this work, β-Ga2O3 films have been grown on the c-plane sapphire substrates by molecular beam epitaxy and annealed in different conditions, the crystalline quality and texture of the β-Ga2O3 thin films before and after annealing were investigated by X-ray diffraction. In order to test the photosensitive properties, each sample are fabricated into solar-blind ultraviolet photoconductors, the effect of different annealing temperature and atmosphere on the photosensitive properties of β-Ga2O3 thin films has been studied. The research results show that a high annealing temperature will make the（4_<sub>02）diffraction peak intensity reduce, resulting in photocurrent and dark current decreased gradually. In addition, the oxygen annealing can reduce fall time of the detector, effectively reduce the persistent photoconductivity effect.（2） The influence of sapphire substrate situ annealing on β-Ga2O3 film quality and performance of solar-blind ultraviolet photoconductors is studied. In order to improve the problem of lattice mismatch between the film and the substrate, this thesis attempts to introduce homogeneous buffer layer between the sapphire substrate and the β-Ga2O3 epitaxial film, because the buffer layer preparation technology is not mature, the quality of β-Ga2O3 film was not obvious to improve. However, the study found that: before the growth of β-Ga2O3 epitaxial films, sapphire substrate sapphire substrate situ annealing can help repair the lattice defects on the surface of substrate which formed in the polishing process and induce the epitaxy of β-Ga2O3 more effective, improve the quality of the films. By make the films into devices, it can also found that, with increase of the films quality, the photocurrent and response of photoconductor will be better, but the dark current of the device also become strong. It will make the light dark current ratio decline. In addition, transient photoresponse of the photoconductor will be effected obviously by the quality of gallium oxide films, with a better films quality, the rise time will be shorter and the falling time will be longer.（3） The scaling properties of β-Ga2O3 solar-blind ultraviolet photoconductors has been discusses. keeping with the film growth process parameters invariable and zoom in or out the solar-blind ultraviolet photoconductors size with proportional, by test the performance of devices with different size, study the effect of device size on the device performance such as optical current, dark current, response and response time. Research results show that: With the reduction of device sizes, the photocurrent of β-Ga2O3 solar-blind ultraviolet photoconductors shows slightly rising tendency and exhibits some nonlinear features, the responsivity of the device will have increased significantly and the time response did not change basically. So, the photoconductors with interdigital electrode structure can be used in large area solar blind ultraviolet detector array after scalling, but with the narrow down of the spacing gap, the manufacture process of the device will become more difficult.（5） A diode assisted photoconductor has been explored. Compared to the interdigital electrode structure, the manufacture process of this device is simpler. With an external zener diode, the difference between the optical signal and the dark signal has been increased. The device structure and the feasibility has been verified in this work and is promising to use in large area solar blind ultraviolet detector array.