Preparation And Performance Study Of Gallium Oxide Thin Films

As a new-type third-generational semiconductor with wide band gap,gallium oxide（Ga₂O₃）has been attracting increasing attention and study in the fields such as ultraviolet light detection and high frequency devices because of its outstanding properties.In this paper,β-Ga₂O₃ thin films on substrates of quartz,silicon and sapphire respectively have been fabricated by using radio frequency magnetron sputtering and tube furnace thermal annealing together.Analysis and measurement such as X-ray diffraction（XRD）,scanning electron microscope（SEM）and UV-Vis spectrophotometer（UV-Vis）have been realized to characterize the crystallinity,microscopic morphology and optical properties of thin films in order to study and determine the influence of technological parameters of radio frequency magnetron sputtering and thermal annealing.MSM solar-blind photodetector was fabricated with standard photolithography and lift-off techniques to study the optoelectronic property of β-Ga₂O₃ thin films.Main contents of this paper includes:Preliminary exploration for the basic technological parameters of β-Ga₂O₃ thin film fabrication using radio frequency magnetron sputtering and thermal annealing has been achieved by employing amorphous quartz substrates.The influences of technological parameters on structural and optical properties of thin films has been studied with a series of experiments.Crystallization orientation of thin films has been determined by XRD.Grain sizes were obtained after calculation;Deposition rate of thin films was obtained with cross-sectional morphology using SEM.Optical transmittance of thin films was obtained by UV-Vis,therefore study of optical band gaps was realized.Optimized basic technological parameters of thin film fabrication is: room temperature of sputtering substrate temperature,5 sccm of sputtering oxygen flow,1 Pa of sputtering pressure,170 W of sputtering power.The optimized annealing time is 120 min.Further exploration for the basic technological parameters of β-Ga₂O₃ thin film fabrication using radio frequency magnetron sputtering and thermal annealing has been achieved by employing silica substrates with（100）orientation.The as-deposited Ga₂O₃ thin films on quartz substrates without intentional heating using radio frequency magnetron sputtering are amorphous,thus high temperature thermal annealing impelled crystallization of β-Ga₂O₃.Main crystallization orientations of β-Ga₂O₃ thin films are（400）and（7 12）.Increasing sputter power enhanced crystallization firstly,then crystallization became weaker to some extend with excessive sputter power.The optimized sputter power is 180 W.Increasing sputter pressure enhanced crystallization firstly,then crystallization became weaker to some extend under excessive sputter pressure.The optimized sputter pressure is 2 Pa.Increasing sputter oxygen flow weakens crystallization.The optimized sputter oxygen flow is 2 sccm.Fabrication of β-Ga₂O₃ thin films on sapphire substrates was realized using optimized technological parameters which were obtained from experiments of quartz substrates and silica substrates.The fabricated β-Ga₂O₃ thin films possess high crystal quality with preferred orientation of（2 01）.The Fabricated MSM photodetector employing films deposied on sapphire substrate exhibits outstanding performance on deep ultraviolet light detecting.Under 10 V applied bias,photodetector is sensitive to 240 nm ultraviolet light with maximum responsivity of 0.63 A/W and external quantum efficiency of 323 %.Under larger applied bias of 30 V,maximum responsivity reaches 3.64 A/W with external quantum efficiency of 1868 %.