Theoretical analysis of low-threshold avalanche effect in WSe₂ stepwise van-der-Waals homojunction photodiodes

In this work, we report simulation-assisted analysis of a room-temperature (300 K) low-threshold avalanche photodiode (APD) based on a WSe₂ homojunction. Device simulations were conducted using a two-band model and the Chynoweth formalism for impact ionization, with material parameters extracted for few-layer and multi-layer homojunction WSe₂ structures. The simulated results accurately reproduce experimental dark and photocurrent characteristics, with an avalanche threshold voltage of approximately
~1.6 V-over 26 times lower than that of conventional InGaAs APDs. The structure exhibits ultra-low dark current (10–100 fA) and high sensitivity, enabling detection of optical signals as low as 7.7 × 10⁴ photons. The analyzed low voltage avalanche photodetector enables utilization in a wide range of applications.