| In recent years,gallium oxide(Ga2O3)has attracted more and more attention in the development of semiconductor industry.Due to its excellent material properties,Ga2O3 has shown great development prospect and application potential in the preparation and research of optoelectronic devices and high-frequency high-power power electronic devices.It has a bandgap of 4.9 eV,its theoretical breakdown electric field strength is expected to be as high as 8 MV/cm,and the Baliga's figure of merit is about 3444.Due to its many properties,it occupies a great advantage in the preparation of wide bandgap semiconductor devices.The absorption edge of Ga2O3 is located at the center of the solar blind region,making it one of the best materials for the preparation of solar blind photodetectors.More importantly,the single crystal of Ga2O3 can be prepared by the traditional melting method,which broadens the road for it to compete in the wide bandgap semiconductor materials and devices in the future.In this paper,the main research work is focused on fabrication of Ga2O3 single crystal solar blind photodetector and the study of the photodetector performance.First,we used vacuum high-temperature treatment and Sn closed tube diffusion to improve the conductivity of the existing semi-insulated Ga2O3 single crystal in our group as the basis of subsequent photodetector preparation.In the experiment of vacuum high temperature treatment and Sn closed tube diffusion,the electrical properties of semi-insulated Ga2O3 single crystal have been effectively improved,but there are still some problems on the surface of treated Ga2O3 single crystal,which cannot meet the requirements of subsequent device preparation.Therefore,we selected n-Ga2O3 single crystal with carrier concentration of 1 × 1017/cm3 to conduct preparation and performance optimization of the solar blind photodetector,and studied the performance of Ga2O3 solar blind photodetector at high temperature.The research of this paper mainly includes the following four aspects:(1)Vacuum annealing was used to improve the conductivity of semi-insulated Ga2O3 single crystal,Hall measurement results showed that the electrical properties of semi-insulated Ga2O3 single crystal samples changed to a certain degree after 800 ?vacuum annealing,when the annealing temperature was further increased to 900 ?and 1000 ?,the change of electrical properties was more obvious.However,the results of X-ray diffraction(XRD)and atomic force microscope(AFM)showed that the annealing treatment at a higher temperature caused damage to the crystal quality and surface morphology of the samples,resulting in the appearance of cracks on the surface and the occurrence of local regional crystal orientation.In terms of electrical property stability,the sample after 800 ? annealing was restored to semi-insulating state after one week,while the electrical properties of the samples treated at higher temperature were relatively stable.X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy(Raman)were used to confirm the mechanism of Ga2O3 single crystal's electrical properties in high temperature vacuum environment,the change of electrical properties was caused by the increase of oxygen vacancy content in Ga2O3 with the increase of annealing temperature.(2)Closed tube diffusion was used to semi-insulated Ga2O3 single crystal for Sn doping,Hall measurement results show that the electrical properties of Ga2O3 single crystal after 800 ? diffusion treatment have changed significantly,the change degree was basically consistent with the results obtained at a higher diffusion temperature.The results of XRD and AFM showed that the diffusion of Sn closed tube could effectively inhibit the crack and crystal orientation of Ga2O3 single crystal in the vacuum annealing experiment.The state of Sn in Ga2O3 was analyzed by XPS.Sn presented as+4 valence in Ga2O3 at a lower diffusion temperature,but gradually changed to +2 valence with the increase of diffusion temperature.The influence of diffusion temperature on the impurity state of Sn was analyzed by using photoluminescence(PL).With the increase of diffusion temperature,Sn gradually transformed from donor to acceptor and the content of donor-acceptor pair increased.(3)Thermal vacuum evaporation was used to form Cu Schottky contact and Ti/Au ohmic contact on the surface of Ga2O3 single crystal to prepare the vertical structural Ga2O3 solar blind photodetector,the forward and reverse I-V characteristics and time-dependent photoresponse were tested and analyzed,exhibited a higher rectification ratio of up to 5 x 107 at ±2 V,the time dependent photoresponse spectra indicated the high reversibility and high reproducibility of the Ga2O3 solar-blind photodetector.Photoresponse spectra were performed to investigate the solar blind wavelength response selectivity of the photodetector,the Ga2O3 solar-blind photodetector showed obvious response to solar blind UV light even at zero bias,which proved the Cu/Ga2O3 SBD solar blind photodetector can work as self-powered detector.Meanwhile,the photodetector showed a sharp cutoff wavelength at 256 nm,which indicated the detector had an excellent solar blind response selectivity.(4)Cu/Ga2O3 solar blind photodetector was optimized and porous structural Schottky electrode was prepared.The responsivity of the optimized photodetector was 1000 times higher than that before the optimization.The electric field in the depletion region of the photodetector is studied by simulation,and the red shift of the peak position of responsivity with the increase of reverse bias was analyzed.I-V characteristics and time dependent light response testing of the high temperature performance of the optimized detector were studied under different temperature.The photodetector showed significant response to 253 nm UV light and a rapid and stable periodic response in the time dependent spectra from room temperature to 85.8?,which proved that the optimized photodetector had a certain high temperature tolerance. |
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