Self-Biased Mo/n-4H-SiC Schottky Barriers as High-Performance Ultraviolet Photodetectors
Sandeep K. Chaudhuri, Ritwik Nag, Krishna C. Mandal
Abstract
We report a high photocurrent-to-dark current ratio (PDCR) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${8}\times {10}^{{5}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\mu \text{m}$ </tex-math></inline-formula> thick n-type 4H-SiC epilayer with an effective doping concentration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{14}}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{3}}$ </tex-math></inline-formula> and low trap concentration. The SBDs demonstrated a built-in voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {bi}}$ </tex-math></inline-formula> ) of 2.48 V as measured from capacitance-voltage characteristics with a test frequency of 1 MHz. A hole diffusion length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{d}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22.8\mu \text{m}$ </tex-math></inline-formula> was calculated using a drift-diffusion model applied to alpha radiation response of the SBDs. Such high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {bi}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{d}$ </tex-math></inline-formula> 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.