Research Of UV Photodetectors Base On GaN Materiels

There are many areas of application using ultraviolet detection. These includeflame and heat sensors,missile plume detection, and secure-from-earth inter-satellitecommunications. The AlGaN is direct bandgap semiconductor.Its bandgap can betailored from3.4eV to6.2eV, corresponding to a band-edge wavelength range of365nmto200nm, which covering the entire solar-blind band.AlGaN is an ideal material for UVdetector. This article refer to the research of AlGaN based UV detectors,includingstructure design,material growth,device fabrication and testing analysis.To achieve real solar blind detection, the Al fraction of intrinsic AlGaN should begreater than0.46.The thickness of intrinsic AlGaN should be300nm to obtain higherquantum efficiency and faster response. On this basis, we design the material structureof PIN and MSM UV detectors.In order to improve the quality of AlGaN on sapphire, we used the LT/HT AlNgrowth method, obtaining high quality AlN template.For AlN,the x-ray ω（002） FWHMof AlN is74arcsec,and the rms of surface is0.33nm. By optimizing the processparameters such as growth temperature, pressure and Ⅴ/Ⅲ ratio, the high qualityAlGaN material was obtained. For Al_0.46GaN,the x-ray ω（002） FWHM is223arcsec,ω（102） FWHM is783arcsec,the surface is smooth,and the transmission spectrum hassharp band edge at278nm. Through the experiment, the hole concentration of P-GaNreached3.1×10¹⁷cm^-3by annealing at an optimized temperature750℃.In the PIN device fabrication prosess,a two steps ICP etching meteod was used toobtain smooth surface.we also optimized the surface treatment and annealing processfor the n type and p type ohmic contact.Both the specific contact resistance of n typeand p type reached10^-4 cm²magnitude. In the MSM device fabrication prosess,weused annealing method to reduce the leakage current of the device.Afer fabricationprosess,we tested the I-V and spectral response characteristic of UV detectors.For PINsolar blind UV detector,with different Al fraction of intrinsic AlGaN,0.46and0.5respectively,the cutoff wavelength of device were280nm and272nm,the peakresponsivity were0.125A/W@272nm and0.121A/W@262nm,the external quantum efficiency were both57%,the peak detectivity were5×10¹³cmHz^1/2W^-1magnitude.ForMSM UV detector,the Al fraction of absorption layer was0.35,the cutoff wavelengthwas304nm,the peak wavelength was290nm.The MSM device showed optical gainphenomenon,which was caused by trap effect of surface states.