Preparation And Characterization Of β-Ga₂O₃ Thin Films

β-type gallium oxide is a direct wide bandgap transparent oxide material. In the visible region to the ultraviolet region has a high transmittance, with the bandgap of around 4.9eV, it has good physical and chemical stability. Gallium oxide material has been applied in the field of gas-sensitive detectors, UV detectors and electroluminescent light emitting devices. Due to the advantages of the bandgap, gallium oxide has great development potential in the field of power devices. The growth and properties research of gallium oxide thin films are the prerequisite for the preparation of gallium oxide devices. PLD technology can be used in the growth of thin films with high temperature and low vacuum, which is flexible. In this paper, β type gallium oxide thin films were prepared on sapphire and β-Ga₂O₃ substrate by PLD. The crystal structure, growth mechanism and optical properties of Ga₂O₃ films were discussed.Firstly, Ga₂O₃ thin films were grown on a-Al₂O₃ substrates by PLD. We study the effects of technological parameters, which include oxygen partial pressure and temperature, on the crystal quality, surface morphology and thickness of Ga₂O₃ films. With the increase of oxygen partial pressure, the crystal quality of the films increased and the surface roughness decreased, the growth rate of the film increased, the ratio of O/Ga increased. Substrate temperature has little effect on the crystallization of Ga₂O₃ films, and the growth rate decreases with the increase of temperature.Secondly, preparation device requires the crystalline quality of the films to be better, and roughness low. According to the growth rules in the front, to determined the PLD preparation technological parameters of film: 600℃ of substrate temperature,0.01 mbar of oxygen pressure, 5cm of the distance between target and substrate, 3Hz of laser pulse frequency, 2J/cm2 of the laser energy density. The epitaxial relationship, interface properties, chemical and growth patterns of Ga₂O₃ films were studied. The epitaxial relationship of Ga₂O₃ thin films grown on Al₂O₃ is α-Al₂O₃（0001） || Ga₂O₃（ 2 01）, β-Ga₂O₃（010） | α-Al₂O₃（1100） and β-Ga₂O₃(102||α-Al₂O₃（11 2 0）. Due to the rotational symmetry of sapphire, triple domain structure forms in Ga₂O₃ films. Three kinds of chemical states of gallium existed in the films that were prepared in the condition of low oxygen partial pressure（0.0013mbar）. Because of the large lattice mismatch between β-Ga₂O₃（ 2 01） and α-Al₂O₃（0006）, there are a large number of dislocations in the interface. The growth pattern of the films is three-dimensional growth.Thirdly, the photoluminescence properties and mechanism of photoluminescence of β-Ga₂O₃ thin films grown under the condition of oxygen partial pressure of 0.01 mbar were studied. The temperature and power dependence of the PL spectrum of β-Ga₂O₃ thin films were measured. Three peaks were obtained by using Gaussian fitting in 582.7nm, 517.1nm and 437.4nm in invisible region of photoluminescence. Through analysis of the peak shift and intensity change with power dependence luminescence, mechanism in visible region was the donor acceptor pair recombination transmission. Oxygen vacancy contributed to blue luminescence, and gallium vacancy contributed to green luminescence. The transmission result shows that the transmittance of Ga₂O₃ is about 85% in the visible region and 80% in the UV region. The bandgap of the film can be calculated by（αhv） 2 vs. hv curve, and the result is 5.0eV.Finally, homoepitaxial β-Ga₂O₃ films were prepared by PLD. By XRD analysis, the film were a single crystal, and the quality of the film were better than that of the substrate on（100） direction. But compressive stress existed in the film, which made the peak shift of XRD 2θ, rocking curves and reciprocal space map. Through analysis, for the compressive measurement was due to the oxygen vacancies in the films, which lead to the lattice constant increase +0.8%. The morphology of the film showed trend of the two dimensional growth modes.