The Research On Spectral Response Of 4H-SiC Avalanche Photodiodes

High-performance UV photodetector is the key section of UV detection,which is used in many applications of military and civilian fields.Due to the excellent physical performance,wide bandgap and mature growth process,4H-SiC becomes the potential material of high-performance UV photodetector.Many research groups focused on the4H-SiC avalanche photodetector,because of the low dark current,high quantum efficiency and photocurrent gain.In this paper,the research on spectral response and the preparation processes of 4H-SiC APD UV photodetector are presented,and a 4H-SiC p-i-n UV photodetector has been fabricated.The achievements are as followed:Firstly,the physical model of the device was established and the photoelectric characteristics of the device were simulated in the simulation software named“Sentaurus”.The effects of n⁺-type epitaxial layer,n-type epitaxial layer,n^--type epitaxial layer and p⁺-type epitaxial layer on the spectral responsivity and peak response wavelength were investigated.It was found that the spectral responsivity and peak response wavelength will change with doping concentration and thickness of these epitaxial layers.After the study,the appropriate doping concentration and thickness of these epitaxial layers and structure of the device were determined.Secondly,the preparation processes of 4H-SiC APD were studied.The preparation processes were consisted of several single step processes including the RCA cleaning,metal deposition and lift-off,thermal oxidation and ICP dry etching,and the details and parameters of experiment were presented.In the experiment,the new metallization schemes based on Ti/Al/Ni/Au multilayers was used as the p-type ohmic contact metal,and the contact resistivity was 8.5×10^-4?cm² when the contact resistivity of Ti/Al/Au was3.1×10^-3?cm².The effect of Ni layer on p-type ohmic contact was analyzed.Thirdly,according to the study of the preparation processes,a 4H-SiC p-i-n UV photodetector was fabricated and characterized.The dark current was nearly 3 p A level,and keep same value as the reverse voltage increasing from 1V to 10V.The wavelength at peak response was about 275 nm,and the UV-visible rejection ratio was over 1000.The results demonstrated that this 4H-SiC p-i-n UV photodetector can work well in the UV range,and the design of the preparation processes was successful.