A Novel 4H-SiC UV Photo-Transistor based on a Shallow Mesa Structure

In this paper we report the first experimental results of a novel 4H-polytype Silicon Carbide Ultra-Violet Photo-Transistor. It is a vertical structure based on a shallow n-Type mesa surrounded by a p-Type region. The device has an optical area of 1.015•10-4cm2 and a dark current of 10pA. Under UV radiation in the range between 210nm and 390nm, it shows a maximum dynamic range of 108.5dB and an optical gain of 16365, at a bias voltage of 0.5V and a wavelength of 310nm. On the same wafer, p-i-n vertical photodiodes are also fabricated in order to compare the photo-Transistor performances with a reference device. The p-i-n photo-diode showed a dark current of 4pA, a dynamic range of 42dB, which is 61% lower than that of photo-Transistor, and an external quantum efficiency of 51.3%. The optical gain mechanism is ascribed to the variation of the potential barrier height between Source and Drain terminals due to hole-electron photo-generated pairs, which are efficiently separated by the electric fields of the p-n junctions close to the lighted surface.