Theoretical study of device sensitivity and gain saturation of separate absorption, grading, charge, and multiplication InP/InGaAs avalanche photodiodes

In this paper, we present a theoretical investigation into the performance of a separate absorption, grading, charge, and multiplication InP/InGaAs photodiode (SAGCM) using a two-dimensional drift-diffusion model. The analysis examines the sensitivity of the device performance to variations within the overall geometry of the photodiode. Specifically, we explore modifications to the p⁺ diffusion at the surface of the device, the thickness of the multiplication region, and the relative doping within the mesa charge sheet. It is found that variations within the design specifications may lead to considerable perturbations in the current-voltage response. In addition to the sensitivity analysis, the extent of gain saturation due to space charge effects within the diode is investigated. The effect of gain saturation is observed to agree with analytical based predictions. To the authors´ knowledge, this is the first demonstration of gain saturation due to space charge effects in a SAGCM APD