Study On Photoelectric Properties Of Niobium Doped Gallium Oxide

Ga₂O₃ material has the characteristics of wide bandgap,high saturation electron mobility,high breakdown voltage and excellent radiation resistance.Therefore,Ga₂O₃is very suitable for application in the field of solar-blind detector,luminescent device,power device and photocatalysis.However,the conductivity of Ga₂O₃ at room temperature is very poor,which seriously affects the comprehensive performance of Ga₂O₃ device.Hence,many researchers begin to work on improving the optical and electrical properties of Ga₂O₃ material,and element doping and noble metal nanoparticles modification have been regarded as the most promising strategies.According to the first-principles calculation,niobium（Nb）is regard as the best candidate for transition-metal n-type doping of Ga₂O₃.This is because niobium is a shallow impurity,which might be helpful to improve the electrical properties of Ga₂O₃ material.In this paper,Nb was selected as doping agent,and Nb dopedβ-Ga₂O₃（β-Ga₂O₃:Nb）film was fabricated for the first time.In addition,the effect of Nb doping and Au nanoparticls modification on the optical and electrical properties ofβ-Ga₂O₃:Nb film were investigated.The main contents include:（1）Theβ-Ga₂O₃:Nb thin films have been fabricated by radio frequency magnetron technique.The effects of Nb doping,annealing atmosphere,film thickness and Au nanoparticles modification on the structural and optical properties ofβ-Ga₂O₃:Nb thin films have been investigated.The annealing treatment improves the crystallinity,especially in N₂.The crystalline quality ofβ-Ga₂O₃:Nb thin film is significantly improved when the film thickness exceeds 145 nm.The Au nanoparticles can affect the optical properties ofβ-Ga₂O₃:Nb thin film and decrease the barrier height of theβ-Ga₂O₃:Nb/p-Si heterojunction.In addition,the band gap ofβ-Ga₂O₃:Nb film was affected by the Nb doping,annealing atmosphere,film thickness and Au nanoparticles modification.These results enrich our knowledge of many fundamental properties ofβ-Ga₂O₃:Nb thin films,and provide application guidance forβ-Ga₂O₃:Nb films in optoelectronics area.（2）P-Si/n-β-Ga₂O₃:Nb heterojunctions were achieved by depositingβ-Ga₂O₃:Nb films on p-Si substrates,and theβ-Ga₂O₃:Nb films with Nb doping amounts of 2.1at.%,2.8 at.%and 4.1 at.%were grown on p-si substrate by magnetron sputterin.The forward current of annealed p-Si/n-β-Ga₂O₃:Nb（2.8at%）heterojunction is 35 times larger than that of as-deposited at+15V.The current transport mechanism of the p-Si/n-β-Ga₂O₃:Nb（4.1at%）heterojunctionwas dominated by the recombination tunneling and space charge limited current（SCLC）mechanism.The activation energy ofβ-Ga₂O₃:Nb film was dependent on the Nb concentration,and values for the activation energy of theβ-Ga₂O₃:Nb film with Nb concentration of 2.1 at.%,2.8 at.%,and 4.1 at.%were 1.3 e V,0.75 e V,and 0.65 e V,respectively.The Nb concentration dependence of the activation energy was attributed to the acceptor impurity band forms in the crystal due to high doping levels causing the Nb acceptor wave functions to overlap.（3）β-Ga₂O₃:Nb film was prepared by magnetron sputtering method.For the fabrication of MSM structure photodetector,the interdigital Au electrodes were deposited on theβ-Ga₂O₃:Nb film surface using a shadow mask with the vacuum thermal evaporation technique.The photodetector based on slight trace amount of Nb-dopedβ-Ga₂O₃ film shows outstanding device characteristics.The sensitivity of the fabricated photodetector is higher than 100.The response time are estimated to be0.526s/2.83s and 0.095s corresponding to the rise edge and decay edge of the current,respectively.Nb is a shallow donor and considered as an outstanding dopant for n-type doping ofβ-Ga₂O₃.It can effectively improve the electrical properties ofβ-Ga₂O₃.Besides,the oxygen vacancy decreases with Nb doping.All these can contribute to the high performance ofβ-Ga₂O₃ detector.（4）A series of Au thin layer were deposited on the quartz substrate via DC sputtering and subjected to annealing at 1073 K for 90 minutes,forming the Au nanoparticles decorated quartz substrate.And theβ-Ga₂O₃ films were deposited on the Au nanoparticles decorated quartz substrate by magnetron sputtering method.The Au nanoparticles decoratedβ-Ga₂O₃ films presented a better photocatalytic property than the pureβ-Ga₂O₃ film.The enhanced photocatalytic performance is ascribed to the promotion of charge separation and suppression of charge recombination by blending Au nanoparticles.This is of great significance for the practical industrial application ofβ-Ga₂O₃ film in the field of photocatalysis.