CVD graphene/SiC UV photodetector with enhanced spectral responsivity and response speed

Abstract

A self-powered high-performance graphene/Silicon Carbide (G/4H-SiC) ultraviolet Schottky junction photodetector has been fabricated and the effect of using monolayer and bilayer graphene on the device performance parameters was investigated. P-type graphene sheets were grown by the chemical vapor deposition (CVD) method while 4H-SiC material consists of an epilayer structure of n-/n+ on bulk n-SiC. Two photodetector devices have been studied one with monolayer graphene (MLG) and the other with bilayer graphene (BLG). The proposed photodetector structure reveals the highest spectral responsivity known of a G/4H-SiC UV photodetector so far. Electronic and optoelectronic characterizations were done under an ultraviolet wavelength range from 240 to 350 nm. The results show two spectral responsivity maxima (Rmax) at 285 nm and 300 nm wavelengths. Exhibiting two maxima in spectral responsivity and detectivity is caused by the constructive and destructive interference effects of multiple reflections at the SiC epilayer's interfaces. The photodetector devices exhibit high spectral responsivity (R - 0.09 AW-1) maximum detectivity (D* - 2.9 x 1012 Jones) and minimum noise equivalent power (NEP - 0.17 pWHz-1/2) in both devices. Using bilayer graphene instead of monolayer showed no significant change in both the photogenerated current and the spectral responsivity due to the higher absorption coefficient of bilayer graphene however it exhibited a significant improvement in the response speed. The response speed was found to increase by 50 % when bilayer graphene was used as a hole collecting electrode in the G/4H-SiC junction. This is because bilayer graphene creates a narrower depletion layer and higher electric field which promotes efficient charge separation and recombination.