The Preparation And Photoelectric Properties Of ?-Ga₂O₃ Thin Films

?-Ga₂O₃ is a typically representative of the third generation of semiconductor materials,it's a semiconductor material with wide band gap characteristics.It not only has excellent photoelectronic characteristics,but also has high thermal stability and good chemical stability,it's becoming a viable candidate for certain high-frequency,high-power devices,photodetectors,solar cells,and sensors with capabilities that exceed existing technology.Especially in the field of photodetection,The forbidden band width of gallium oxide corresponds to the solar blind ultraviolet region,which makes up for the shortcomings of Ga N and Zn O due to doping.Ga₂O₃ photodetectors are becoming one of the current research hot spots in the world.However,the existing thin-film growth technology has the disadvantages of high cost or strict process requirements,and there are still major challenges to achieve large-area thin-film growth by feasible methods.In this paper,the main properties of Ga₂O₃ and their applications in devices are reviewed.After comparing different film preparation methods,a simple,low-cost solution spin coating method is selected.The Ga₂O₃ thin film was prepared on the sapphire substrate by gallium nitrate hydrate as a gallium source via spin-coating nethod followed by a post-annealing process.The effects of different process conditions on the crystallization,surface morphology and optical properties of the films were discussed,including solution concentration,annealing temperature and annealing atmosphere.Samples were selected based on the optimal process conditions for electrode deposition for the preparation of photodetectors,and I-V and I-T experiments were performed to prove its feasibility as an ultraviolet photodetector.The specific experimental analysis results are as follows:(1)The effects of solutions with different concentrations on film properties were studied in this paper:the concentrations were changed to 0.1mol/L,0.3mol/L,0.5mol/L,and 0.7mol/L,respectively.X-ray diffraction,scanning electron microscopy,and UV-visible light transmittance spectroscopy experiments were used to characterize and compare the properties of the films.The experimental results showed that when the solution concentration was 0.1mol/L,the sample surface will have poor solution adhesion due to lower concentration,the surface scanning electron microscope image will be blurred,and the particles will be uneven;when the solution concentration was 0.7mol/L,due to excessive concentration causes the surface particles to adhere and crystallize poorly.Scanning electron microscope images showed obvious cluster squeezing and extremely low transmittance.The 0.3mol/L and 0.5mol/L samples showed good crystallinity,.The particles on the surface of the 0.3mol/L sample were more uniform and flat,and showed a transmittance of more than 80%for light with a wavelength above 280nm.It was estimated that the band gap width is 4.92eV,so it was considered suitable to prepare the required Ga₂O₃films at this concentration.(2)The effects of different annealing temperatures on film properties were studied in this paper:spin coating at a concentration of 0.3mol/L,and changing the annealing temperature from 500? to 1100?,X-ray diffraction,scanning electron microscopy,and UV-visible light transmission spectroscopy experiments were used to compare the properties of the films.The experiment found that when the temperature rises to 900?and above,the diffraction peak intensity and the grain size will increase significantly due to the diffusion and the lattice replacement of Al atoms from the substrate,and the band gap width will increase significantly to above 5.2eV;the degree of crystallization was poor at temperatures of 500 and 600?,the surface particles were small,and the image of scanning electron microscope was foggy;Significant particles began to appear on the sample surface from the temperature of 700?.At 800?,the particles are flat and uniform,the transmittance is high,and the forbidden band width is 4.90eV,which is considered to be the best annealing temperature to prepare?-Ga₂O₃film by spin-coating method.(3)In this paper,the effects of different annealing atmospheres on the properties of the films were studied.Based on the previous experiments,the samples were compared at a concentration of 0.3mol/L in an oxygen and air atmosphere at 800? to compare the film properties.Oxygen atmosphere can make up for the oxygen vacancy defects during the film growth process.X-ray diffraction experiments found that the grains of the samples annealed in an oxygen atmosphere have good consistency in grain orientation.X-ray photoelectron spectroscopy experiments show that the number of surface oxygen vacancies is reduced and the surface particle gap is small.AFM experiments have proven that the roughness is smaller,samples have higher transmittance,and wider band gap than the samples annealing in air atmospheres.(4)The electrode was deposited and subjected to I-V test.The light-dark current ratio of the air-annealed sample was 21.44,and the oxygen-annealed sample was31.16.Oxygen-annealed sample had strong anti-noise interference ability,but the performance such as the optical response R_?and quantum efficiency EQE were poor.The oxygen-annealed sample after multiple spin coatings had a response time of 0.1s and a decay time of 0.12s.The fast response speed indicationg that the thin films prepared by the spin-coating method have the good potential for fabricating fast-response photodetecting devices.