Study On Ga₂O₃-Based Ultraviolet Photodetectors

At present,UV detection technology has been widely used in the military and civilian fields.in the military,UV detection technology is often used to detect missiles,rocket engines,aircraft and other artificial radiation sources,analyze their trajectories and provide UV warning.in the civilian field,UV detection technology can be used for flame monitoring,environmental monitoring,UV imaging,UV communication,solar UV spectral analysis,etc.With the continuous advancement of research,the UV detector has developed from the early photomultiplier tube to Si-based UV detector,and then extended to the latest wide-band UV detector.To develop new high-performance wide-band UV detector cannot be developed without the research of wide-band semiconductor materials.After the continuous exploration of wide-band semiconductor materials,a variety of materials have been applied to build UV detector.These materials include a variety of oxide semiconductors such as ZnO,Mg_0.2Zn_0.8O,TiO₂,Ga₂O₃,NiO₂,etc.They have large forbidden band widths,high chemical and thermal stability,and good radiation resistance.Ga₂O₃ is a new ultra-wideband gap semiconductor material,which has been widely used in power electronics,optoelectronics,memory,sensing systems,deep ultraviolet transparent conductive oxide electrodes,photocatalysts and other fields.Ga₂O₃has six isomers,which areα-Ga₂O₃,β-Ga₂O₃,γ-Ga₂O₃,δ-Ga₂O₃,ε-Ga₂O₃ andκ-Ga₂O₃.Among these isomers,there are many studies aboutα-Ga₂O₃ andβ-Ga₂O₃.The gap width ratio ofα-Ga₂O₃ is larger thanβ-Ga₂O₃,up to 5.3e V.When applied to ultraviolet photodetectors,α-Ga₂O₃ has a shorter cut-off wavelength.β-Ga₂O₃ is a direct bandgap wide bandgap semiconductor material.Compared with semiconductor materials with similar bandgap width,β-Ga₂O₃ has a good electron mobility（～100 cm²/V）.However,at this stageα-Ga₂O₃ andβ-Ga₂O₃ is a wide band gap ultraviolet detector developed as a substrate material,usually with low photocurrent and weak response.It is urgent to develop ultraviolet photodetectors with higher photocurrent and greater response.In this thesis,α-Ga₂O₃ andβ-Ga₂O₃ are used as substrate materials to develop new UV photodetectors by synthesizing low-dimensional nanostructures,forming heterojunctions,and doping with other elements.The following research work was carried out:In Chapter 2 of this thesis,The FTO/α-Ga₂O₃/Mg_0.2Zn_0.8O heterojunction UV detector was first designed and prepared as MSM structure usingα-Ga₂O₃ as the substrate material.α-Ga₂O₃ external nanowire arrays and Mg_0.2Zn_0.8O are both well crystallized and strongly absorb UV light,where Mg_0.2Zn_0.8O is uniformly filled in the gaps ofα-Ga₂O₃ nanowire arrays.UV light given to the heterojunction device will generate a large number of photoelectron-hole pairs on the Mg_0.2Zn_0.8O side of theα-Ga₂O₃/Mg_0.2Zn_0.8O heterojunction and separate under the action of the built-in electric field,making the device highly conductive and generating a large photocurrent.Chapter 3 of this thesis,β-Ga₂O₃ is used as the substrate material to design and prepare ultraviolet photodetectors（MSM structure）based on In-doped Ga₂O₃ nanomaterials,including four kinds of contrast devices,in which the doping concentration of In is set at 0%,10%,20%and 30%.The main feature is that with the increase of In doping concentration,the prepared film changes from crystalline state to amorphous state.Thanks to the morphological transformation,the device with the highest concentration of In doping has the largest optical current,but also has the largest dark current.In general,devices with 20%in doping concentration have the highest light-dark suppression ratio（2.8×10³ at 5V bias）,low dark current（8.2n A at 5V bias）,low spectral response（739.2A/W at 260nm）,moderate response recovery time（6.67s response time,4.65s recovery time）,and excellent ultraviolet detection performance.This paper develops FTO/α-Ga₂O₃/Mg_0.2Zn_0.8O heterojunction ultraviolet detector and ultraviolet photodetector based on In-doped Ga₂O₃ nanomaterials.The effects of the synthesis of low-dimensional nanostructures,the formation of heterojunction,and the doping of elements on the device performance were studied,and the specific mechanism of the improvement of photocurrent and responsiveness was explained.This provides a new idea for device performance optimization.