Mg₂Si/Si vertical heterojunction near-infrared photodetector

Mg₂Si, a narrow-bandgap semiconductor, excels in near-infrared (NIR) (700-1700 nm) light harvesting. However, Mg₂Si-based NIR photodetectors (PDs) on silicon show limited response beyond 1100 nm. This study presents a high-performance Mg₂Si/Si vertical heterojunction PD for NIR detection. We investigated the ITO/Mg₂Si/Si heterojunction device using a co-simulation framework that combines FDTD optical and CHARGE electrical models. The structure exhibits strong rectification, significantly reducing dark current. Photoelectrical characterization at 1064 nm demonstrated enhanced photocurrent under zero bias, achieving a responsivity (R) of ≈230 mA/W. Optimal self-powered performance was observed at 1310 nm, with R ≈ 1.2 mA/W, specific detectivity (D^*) ≈1 × 10⁹ Jones, a response time of 73.5 μs, and a 3 dB bandwidth of ≈3.1 kHz. Finally, a proof-of-concept optical communication system successfully transmitted ASCII-encoded data using 1310 nm NIR light, highlighting the device's potential for low-power NIR applications.