Enhanced near-infrared absorption in Au-hyperdoped Si: interplay between mid-gap states and plasmon resonance

Detecting near-infrared (NIR) light with high efficiency is crucial for photodetectors that are applied in optical communication systems. Si hyperdoped with deep-level impurities provides a monolithic platform for infrared optoelectronics with room-temperature operation at telecommunication wavelengths. In this work, we present strongly enhanced NIR absorption via the hybridization between plasmon resonance and mid-gap states in Au-hyperdoped Si layers, prepared by ion implantation and pulsed laser melting. The Au-hyperdoped Si layers exhibit high-quality recrystallization with the substitution of Au atoms into the Si matrix and the formation of Au nanoparticles on the surface. Surprisingly, the Au-hyperdoped Si layers exhibit a NIR absorption with spectral response extending up to 1650 nm and a maximum absorptance up to 30%. According to electromagnetic simulations, the enhanced infrared photoresponse can be attributed to the mid-gap states induced by substitutional Au atoms and the localized surface plasmon resonance associated with the Au nanoparticles. This work presents a simplified one-step process to gain significant enhancement of NIR absorption, which paves a way for the realization of Si-based photodetectors with room-temperature operation and outstanding performance.