Research On Structure And Performance Optimization Of Gallium Oxide Based Photodetector

Compared with the traditional infrared and other photoelectric detection methods,the ultraviolet detector technology of wide band gap semiconductor has incomparable advantages.In the solar blind ultraviolet detection area,its signal detection difficulty is reduced,and the false alarm rate is low.As it belongs to passive detection,which has rare electromagnetic radiation,this mode has good concealment.It can detect the ultraviolet signal source accurately,generated by engine,missile or plasma radiation,as well as good military application value(UV guidance,UV warning,UV interference and UV communication)and civil application value.As a new wide band gap semiconductor material,gallium oxide has become an international research theme in the research of solar blind ultraviolet photo-detectors in recent years,because of its excellent physical properties(wide band gap,strong breakdown electric field,etc).In this paper,taken as the main research object,gallium oxide semiconductor materials are fabricated into different structure types to optimize the performance of the Ga2O3 based photodetectors.According to the different working modes,the device structure of solar blind ultraviolet photo-detectors can be divided into photo-conductive(non junction device),Schottky barrier type,metal semiconductor metal type,p-n junction(heterojunction),pin junction and other types.Based on the main performance indexes such as dark current,photocurrent,responsivity,quantum efficiency and response time,as well as the difficulty and cost of preparation,the following achievements have been achieved:(1)Research of the photoconductive detector:photoconductive detector has the advantages of simple structure,easy process and high internal gain,but the disadvantages are large dark current and low sensitivity.Iron as dopant,due to its high insulation and can raise the Fermi level of the material,requires a large amount of kinetic energy for carrier transport and has the potential to reduce the dark current(noise)of the device.In this paper,we have grown(Fe-doped)Ga2O3 crystal substrate based on EFG technology,and fabricated Au/Ti/Fe-doped Ga2O3/Ti/Au photo-conductive devices.The dark current is optimized and its value is about 10-13A,which is 5-7 orders of magnitude lower than that of the same type of devices.(2)Research of the Schottky barrier photodetector:Schottky barrier photodetector has the advantages of high response,low dark current,high response time,high quantum efficiency,and avoiding p-type.At the same time,compared with the photoconductive device,it has the characteristics of self-power.In this paper,we have grown ?-Ga2O3 substrates based on EFG technology and fabricated Au/Ti/?-Ga2O3/Ni/Au Schottky barrier devices.The device can achieve a large rectifier ratio,low reverse leakage current,and favorable breakdown voltage.It is worth noting that the R,D*,and EQE of the photodetector are 2.875 mA/w,1010 jones,and 1.4%respectively at zero bias voltage,indicating that the photodetector has self-powered application performance.(3)Research of the heterojunction detector:The heterojunction structure with appropriate step migration can accelerate the electron-hole separation transport generated by the photoelectric response,and the heterojunction structure has advantages in dark current,responsiveness,response time,sensitivity,and other aspects.In this paper,we used p-type Pb(Zr0.52Ti0.48)O3(PZT),and n-type Ga2O3 to fabricate PZT/Ga2O3 heterojunction photodetectors by pulsed laser deposition(PLD)and RF magnetron sputtering,respectively.Compared with Ga2O3 photodetector,PZT/Ga2O3 heterojunction photodetector achieves lower Idark,higher PDCR,R,and faster response time.(4)Research of the heterojunction band alignment:Interface information is very important for heterogeneous structured devices.Devices with hierarchical heterojunction structures exhibit many performance advantages such as fast response and low dark current.Therefore,it is of great significance to carry out energy band engineering for the research of heterojunction devices.We fabricated TiO2 and Ga2O3 heterojunctions on sapphire substrates by PLD technique,and then carried out UV-Vis absorption and XPS tests,and analyzed and calculated based on the Kraut model.The ?EV of TiO2 and Ga2O3 is determined to be about-0.6 eV,while the ?EC is about-0.68 eV.The I-band alignment of TiO2 and Ga2O3 heterojunction provides the foundation for further research of photodetectors based on the heterojunction structure.