Growth And Photoelectric Properties Of Gallium Oxide Thin Films

Due to the strong absorption of the stratospheric ozone layer,almost no photons reach the earth's surface from the sun within the cut-off wavelength of less than 280 nm.The solar-blind detector can only detect radiation with the wavelength of less than 280 nm,but is not sensitive to visible and infrared radiation,so it has the unique advantage of low noise and high sensitivity.Ga₂O₃ has the advantages of wide bandgap,excellent optical properties,stable physical and chemical properties.In this paper,the pressure,temperature,oxygen partial pressure and power affecting the preparation of thin film materials were studied in a unified way.The characteristics of thin film were characterized by means of material characterization.Then,the photoelectric properties of the detector were compared,and the following conclusions were drawn:Firstly,Ga₂O₃ was epitaxial grown on the c-surface sapphire substrate by magnetron sputtering method,and the crystal structure,surface morphology,element composition and optical transmittance of the epitaxial Ga₂O₃ thin film at different deposition pressures were compared and analyzed by means of material characterization,and then the fork-finger photoconductive ultraviolet detector was prepared.The results showed that the deposition rate of the epitaxial Ga₂O₃ film at different pressures ranged from 0.3 nm/min to 2.0 nm/min.At the same time,it was found that the roughness RMS of Ga₂O₃ thin film first decreased with the increasing of sputtering pressure,and the pressure increased positively after 25mTorr,which was the result of high-energy bombardment effect and ion collision interaction,but the overall roughness of the thin film was low,and the RMS value was between 2 nm-4nm.The average transmittance of all samples at 280-500 nm was over 80%,the optical absorption edge was around 270 nm,and the maximum optical band gap obtained by 25mTorr samples was 5.01 eV,which was similar to the value discussed in the literature.According to the X-ray diffraction pattern,the Ga₂O₃ thin films at various pressures were all single oriented films with parallel-Ga₂O₃?2^<sub>01?surfaces.The Ga₂O₃ thin films prepared under 25 mTorr were the single epitaxial films with the best crystal quality.At this time of the beta Ga₂O₃?^<sub>201?peak of the minimum FWHM to 0.22°,maximum peak intensity can reach 3500.The XPS test results showed that with the increasing of sputtering pressure,the oxygen vacancy density firstly increased and then decreased.Because the oxygen vacancy at the metal-semiconductor interface had a great influence on carrier transport,when oxygen vacancy density is high,more electrons can be tunneled into the semiconductor through the interface barrier,resulting in greater optical responsiveness.However,photogenic carriers are also easy to be trapped by oxygen vacancy,resulting in a relatively long recovery time for the detector.Studies on the photoelectric performance of the detector show that under the deposition pressure of 25 mTorr,the uv detector has high optical responsiveness?303 A/W?,low dark current?10 pA at 20 V bias?,high light-dark current ratio?>10⁵?,high external quantum efficiency?147628%?and fast response speed??_r=0.52 s,?_d=0.12 s?.Device performance is also competitive in published articles.Secondly:the sputtering pressure was fixed at 25 mTorr,and the parameter variables were set as temperature,power and oxygen partial pressure,respectively.The influence mechanism of oxygen partial pressure,power,temperature and thickness on the performance of the detector was analyzed.Comparative analysis found that different temperature 500?under beta Ga₂O₃?2^<sub>01?peak of the minimum FWHM,maximum peak intensity at the same time.From AFM,it can be seen that the surface of gallium oxide thin film was in island shape at low temperature,and transited to polycrystalline shape after the temperature increased,which is consistent with the epitaxial growth mechanism of the thin film.It can be seen from the ultraviolet visible light absorption spectrum that the transmittance of the deposited film at 180 W power is reduced to less than 1%under the ultraviolet light at 200nm.At the same time,when the power is reduced,the absorption edge blue shift of the film is found,which may be the effect of quantum size effect.Through the oxygen partial pressure experiment can show the reduction of a large amount of oxygen vacancy in the film,the change of the oxygen partial pressure will bring light to dark current decline at the same time,the oxygen atmosphere the light of the epitaxial film dark current is much smaller than no oxygen,it's because gallium oxide thin film that has been under oxygen atmosphere inside are lack of oxygen vacancy,leading to significantly reduce the carrier density,which reduces the film conductivity,causes the thin film optical current is very small.This method can be used to study ways to reduce the dark current to improve the light dark current ratio.