Study On Gallium Oxide Heterotype Heterojunction Photodetector

As a new generation semiconductor material,Ga₂O₃ has attracted much attention from UV detector researchers because it naturally corresponds to the band gap（4.9 e V）of the ultra-violet solar blind band and exhibits ideal characteristics of ultraviolet active materials.In the field of ultraviolet optoelectronic devices,in order to meet the needs of energy saving,miniaturization and high efficiency of photodetectors,self-powered systems have become a goal widely pursued by researchers.As a common structure of photovoltaic detectors,p-n junction has become the first choice for solar blind detector researchers.However,no ef-fective method has yet been found to achieve p-type doping of Ga₂O₃,so it is particularly critical to find p-type materials suitable for forming a p-n heterojunction with Ga₂O₃.In current literature reports on Ga₂O₃ heterojunctions,p-type materials have the problem that the processing temperature is not compatible with Ga₂O₃.The only option is to prepare Ga₂O₃first and then process the p-type material,which will sacrifice the effective light ab-sorption area of Ga₂O₃and reduce device performance.As a natural p-type semiconductor material,CuAlO₂has a processing temperature which is compatible with Ga₂O₃,and is ex-pected to solve the above problems.However,there are almost no relevant reports on the research on CuAlO₂and Ga₂O₃heterojunctions,so there are a lot of issues that need to be studied about Ga₂O₃/CuAlO₂heterojunctions.The main research contents of this article on Ga₂O₃/CuAlO₂heterojunction ultraviolet solar blind detector are as follows:1.The electronic structure and correlation of the Ga₂O₃/CuAlO₂heterojunction were studied through the first-principles calculation method.By calculating the binding energy,differen-tial charge density,Bader charge,electron localization function,plane electrostatic potential energy,partial density of state and other parameters of the heterojunction interface,a com-prehensive analysis was conducted on the stability and electron transfer of different interface models.The results show that the stability and electron transfer effect of Ga₂O₃combined with the TO_Cuterminal of CuAlO₂are the best.The band structure of the heterojunction and the built-in electric field at the interface are beneficial to the separation of photogenerated electron-hole pairs.The heterojunction has great potential for application in ultraviolet solar blind detectors.These studies lay the foundation for further exploration of ultraviolet solar blind detectors based on Ga₂O₃/CuAlO₂heterojunction.2.Ga₂O₃,CuAlO₂ and heterojunction films were prepared using the sol-gel method.Through testing,it was found that the heterojunction has a nested energy band structure.The results are in good agreement with the theoretical calculation results.A Ga₂O₃/CuAlO₂heterojunc-tion detector and a MSM structure detector based on Ga₂O₃thin film were simultaneously prepared.Compared with the MSM device,the photocurrent-to-dark current ratio increased from 397 to 1018,the responsivity improved from 5.23 m A/W to 12.12 m A/W,the detec-tivity increased from 9.74×10 Jones to 2.38×10 Jones,and the linear dynamic range ratio improved from 51.96 d B to 60.16 d B at a bias voltage of-15 V,and the performance has been greatly improved.In addition,the Ga₂O₃/CuAlO₂heterojunction detector also shows good self-powering characteristics.When the voltage is 0 V and the illumination is 680μW/cm²,the detector obtains a photo-to-dark current ratio of 445 and a responsivity of 0.23m A/W,a detectivity of 2.17×10 Jones and a linear dynamic range ratio of 52.98 d B.The results show that the Ga₂O₃/CuAlO₂heterojunction has great application potential in the ap-plication of ultraviolet solar blind detectors,providing a new strategy for the development of high-performance solar blind detectors.3.Solutions to further optimize the performance of Ga₂O₃/CuAlO₂heterojunction detectors are discussed.The discussion started from two perspectives:improving the conductivity of the film through appropriate doping to increase the photocurrent of the device,and allowing the electrode to form a good Ohmic contact to reduce the contact resistance to increase the photocurrent.In terms of doping,we theoretically and systematically studied the effects of Si,Ge,and Sn IV group element doping on the photoelectric properties of Ga₂O₃.By calcu-lating parameters such as lattice distortion,electron localization function,formation energy,state density,absorption spectrum,mobility and electron non-radiative capture rate,it was found that Ge-doped Ga₂O₃has the smallest lattice distortion,the largest mobility,the largest conductivity,the minimum electron capture rate,and the smaller absorption edge blue shift.Therefore,Ge doping is more suitable for the application of Ga₂O₃in the field of optoelec-tronics.In terms of Ohmic contact,we focused on the formation mechanism of Ga₂O₃Ohmic contact.Through experiments and calculations,we found that oxygen diffusion plays a cru-cial role in the formation of Ohmic contact in Ga₂O₃.Specifically,the direct contact between Ti and Ga₂O₃is initially a Schottky contact and transforms into an Ohmic contact after rapid thermal annealing（RTA）.It was also observed that oxygen atoms diffused from Ga₂O₃into the Ti layer after RTA,causing Ti to be oxidized to the+3 valence state.Subsequently,den-sity functional theory was used to construct multiple interface models.Analysis of charge density,partial density of state,plane electrostatic potential energy,and I-V characteristic calculations showed that oxygen diffusion lowered the interface barrier and enhanced the electron tunneling effect,resulting in Ohmic contact formation.The trends of experimental results and calculated results are in good agreement.This study provides valuable insights into further optimizing the performance of Ga₂O₃/CuAlO₂heterojunction UV solar blind detectors,and may also have a certain impact on the development of other high-performance Ga₂O₃ electronic devices.