Fabrication Of MSM Solar-blind Ultraviolet Photoconductors Based On Gallium Oxide Thin Films

In recent years,the research on solar-blind ultraviolet detection technology has developed fast.?-Ga₂O₃,with a band gap of 4.9 e V,exhibits excellent optical properties,chemical stability,and high mechanical strength,and thus is a good UV-sensitive material.In this work,the MSM?metal-semiconductor-metal?solar blind ultraviolet photodetectors were fabricated based on the ?-Ga₂O₃ thin films,which were grown by molecular beam epitaxy.MSM photodetector has the advantages of simple preparation,high responsiveness,and good compatibility with CMOS.The specific contents of the paper are as follows:In this paper,the effect of metal-semi-contact on the performance of the device is studied.First,we studied the effect of Ti/Au electrode and Au electrode on the performance of the device.Compared with the device using Au electrode,The performance of the device using Ti/Au electrode is better.So,we use Ti/Au as metal electrode material to prepare gallium oxide MSM solar blind ultraviolet detector.On the basis of this,in order to explore the influence of metal-semi-interfacial properties on the performance of the device,the effect of rapid annealing of the electrode on the performance of gallium oxide MSM device was studied,and its influence mechanism was discussed.The Ti-Au electrode was annealed at 400 ?,500 ?,600 ? and 700 ?,respectively,and the I-V and time-response characteristics of the devices were measured,the microscopic characteristics of the interface were analyzed by SIMS and XPS.The results show that after the rapid annealing,Ti atoms diffused into the surface of gallium oxide to form TiO2.On the one hand,this can reduce the interface of metal-semi-contact barrier height;on the other hand,this also lead to a higher concentration of oxygen vacancies near the interface of gallium thin film and improve the carrier concentration at interface barrier,both photo and dark current of the device will increase with the rise of annealing tempera ture,thereby improving the device's optical responsivity.However,oxygen vacancies have the trap effect,which can leads to a more severe continuous photo-conductivity?PPC?of the device,and the device's response speed deteriorates.Based on the study of metal-semi-contact characteristics,in order to improve the photoresponsivity of the device,the photoelectric properties of(In_xGa_1-x)₂O₃ were studied.In this paper,the relationship between indium incorporation and In source temperature was first explored,and the properties of the films were characterized by EDS,AFM,XPS,UV spectroscopy and so on.The results of EDS show that when the substrate temperature is fixed at 760 ?,and the source temperature is 700 ?,the In source content is 11.5 %,which means that the In source concentration in the(In_xGa_1-x)₂O₃ film can be effectively controlled by In temperature.In order to study the properties of(In_xGa_1-x)₂O₃ thin films prepared by different In source temperatures,the I-V characteristics,time-response characteristics and UV spectra of MSM photoconductive devices were studied.The results show that when the source temperature is below 600 ?,the device performance does not change significantly.When the source temperature is 650 ?,the performanceof the device are obviously improved.However,when the In source temperature is 700 ?,the overall performance of the device is worse,the dark current is 9.8 mA,the photocurrent is 10.3 mA,although the response reaches 7.1×104 A/W,photo and dark current ratio is only 1.0.The results of AFM and XPS analysis showed that the In₂O₃ phase was formed on the surface,which indicated that:(In_xGa_1-x)₂O₃ film has serious crystal phase separation,resulting in poor device performance.Due to the high volatility of In,the In content in the film is not only related to the In source temperature,but also affected by the substrate temperature.In order to weaken the crystal phase separation of the film,the substrate temperature and In source temperature are optimized by a large number of experiments.(In_xGa_1-x)₂O₃ device has a better overall performance.The dark current is 424 pA,the photocurrent is 1.06 ?A,the ratio of light to dark is 2.5×103,and the responsivity is 73.6 A / W.