Fabrication And Spectral Response Characterization Of 4H-SiC P-i-n Ultraviolet Photodetectors

Ultraviolet photodetectors are widely used in military,environmental,Biological Sciences and other fields.4H-SiC is an ideal material for preparing ultraviolet photodetectors because of its wide band gap,high thermal conductivity,high critical breakdown field strength,radiation resistance and corrosion resistance.Compared with 4H-SiC Schottky,MSM,APD and other device structures,with the advantage of embodied intrinsic layer,4H-SiC p-i-n ultraviolet photodetectors have high light absorption efficiency,fast response speed and low dark current,which occupies the mainstream position in practical applications.In this paper,based on the theoretical calculation of the optical absorption coefficient of 4H-SiC materials,the peak responsivity and peak response wavelength of 4H-SiC p-i-n ultraviolet photodetectors were calculated when the thickness of p⁺-layer is changed?the thickness of I-type layer is fixed?and I-layer is changed?the thickness of p⁺-type layer is fixed?,respectively,and the results were analyzed.It is concluded that both a relative thin p⁺-type contact layer and a thick I-type layer should be employed to achieve a high responsivity.Besides,for 4H-SiC p-i-n ultraviolet photodetectors,I-type layer play a more important role on the peak responsivity,while p⁺-type layer will play a relatively more crucial role on the peak wavelength.By optimizing devices' structure and fabrication process,4H-SiC p-i-n UV PDs with four different epitaxial layer thicknesses with low dark current(about 8×10^-10 A/cm² while being biased at a reverse voltage not higher than 10 V)were designed and fabricated in this Letter.The highest peak responsibility of four fabricated 4H-SiC p-i-n ultraviolet photodetectors was 0.139 A/W at 278 nm,corresponding to 62%external quantum efficiency.The response spectra of four samples were calculated theoretically and compared with the experimental results.The calculated results agree with the experimental ones,which proves that the theoretical calculation method is basically correct and the device fabrication is successful.The effect of epitaxial layer thickness on the spectral characteristics of 4H-SiC p-i-n ultraviolet photodetectors was verified experimentally.