Performance Improvement Of Ga₂O₃-based Photodetectors Via Oxygen Vacancy Defects And Electrode Structures

Solar-blind ultraviolet（UV）photodetectors have attracted extensive attention of researchers due to their critical application prospects in military and civilian fields in recent years.Solar-blind UV photodetectors based on wide-bandgap semiconductor materials have become a new generation of UV detection devices.Among these wide-bandgap semiconductor materials,Ga₂O₃ is considered as one of the most ideal materials for solar-blind UV photodetection due to its suitable direct bandgap of～4.7-5.2 e V,high visible-transparency,high radiation hardness,excellent chemical and thermal stabilities,exhibiting the great application potential.At present,photodetectors based on Ga₂O₃ materials have achieved rapid development.However,there are following problems in practical applications:Firstly,Ga₂O₃ thin films are usually accompanied by a large number of intrinsic defects related to oxygen vacancies,which seriously affect the performance of Ga₂O₃-based solar-blind UV photodetectors.Secondly,the inhomogeneous electric fields caused by traditional planar electrodes and the opacity of metal electrodes also severely limit the performance improvement of Ga₂O₃-based solar-blind photodetectors and their applications in the field of transparent electronics.In view of the above scientific problems,this paper aims to realize high-performance solar-blind UV photodetectors,and conduct related research around the suppression of oxygen vacancy defects in Ga₂O₃ materials and the design of electrode structures in UV photodetectors.The main results were obtained as follows:（1）The Ga₂O₃ film was epitaxying grown by MOCVD,and the effects of annealing and plasma treatment on the optical,electrical and optoelectronic properties of the films were systematically studied and the corresponding mechanisms were clarified.It is found that the crystal structure,surface morphologies and light absorption characteristics of Ga₂O₃ thin films have almost no obvious changes before and after treatment.And there is obvious improvement effect on the electrical and photoelectric characteristics such as dark currents and photocurrents of the thin films.Among them,oxygen annealing at 750°C for 40 minutes and oxygen plasma treatment for 10 minutes can both increase the photocurrents and responsivity,and reduce the dark currents by more than one order of magnitude,and the improvement of the electrical and photoelectric characteristics of the film is related to the reduction of oxygen vacancy-related defects and modification of the surface states（2）The Ga₂O₃-based MSM-type solar-blind UV photodetector with the planar electrodes structure was prepared,and the performance of the device was significantly improved by combining the high-temperature oxygen annealing and oxygen plasma treatment.Such as a dark current of～29 p A at 10 V,a UV/visible light rejection ratio(R_peak/R₄₀₀)of 8.6×10⁶,a normalized photo-dark current ratio（NPDR）of 1.3×10¹² W^-1and a specific detectivity of 9.0×10¹⁴ Jones,the comprehensive performance of the photodetector has reached the leading level of similar photodetectors.The excellent performance of photodetectors,such as the low dark current and high UV/visible rejection ratio can attributed to the suppression of oxygen vacancy defects and surface modification during annealing and plasma treatment.（3）The Ga₂O₃ thin film was directly and selectively grown on the sapphire substrate with ITO transparent interdigitated electrodes,and the transparent Ga₂O₃-based MSM-type solar-blind UV photodetector with embedded electrodes was constructed.The transmittance of the prepared photodetector in the visible region is over 80%,indicating its application prospect in the field of transparent electronics.At the same time,the photodetector exhibits the excellent performance such as a low dark current（0.57 p A@10 V）,a high NPDR(1.4×10¹³ W^-1),an excellent UV/visible rejection ratio（2.1×10⁶）and specific detectivity(1.3×10¹⁵ Jones).The main reasons for the high performance of the device are the uniform parallel electric field formed by the embedded electrodes,the high crystalline quality Ga₂O₃ film and the preparation process without etching.