Self-Biased Mo/n-4H-SiC Schottky Barriers as High-Performance Ultraviolet Photodetectors

Abstract

We report a high photocurrent-to-dark current ratio (PDCR) of ${8}\times {10}^{{5}}$ observed in Mo/4H-SiC Schottky barrier diodes (SBDs) in self-biased mode when exposed to a 1.5 mW ultraviolet (UV) emitting at 365 nm. Such high performing self-biased UV photodetectors are poised to address the longstanding problem of designing self-powered UV sensors for harsh environment applications e.g., advanced nuclear reactors and space missions. The vertical Schottky diodes have been fabricated by depositing semi-transparent molybdenum anode contact on $20\mu \text{m}$ thick n-type 4H-SiC epilayer with an effective doping concentration of $10^{{14}}$ cm $^{-{3}}$ and low trap concentration. The SBDs demonstrated a built-in voltage ( ${V}_{\textit {bi}}$ ) of 2.48 V as measured from capacitance-voltage characteristics with a test frequency of 1 MHz. A hole diffusion length ( ${L}_{d}$ ) of $22.8\mu \text{m}$ was calculated using a drift-diffusion model applied to alpha radiation response of the SBDs. Such high ${V}_{\textit {bi}}$ and ${L}_{d}$ led to an excellent charge collection efficiency of 70% and the large PDCR at 0 V applied bias (self-biased mode). The results presented in this letter reveal the unexplored potential of wide bandgap semiconductors as high-efficiency self-biased UV photodetectors.