Dark current in monolithic extended-SWIR GeSn PIN photodetectors

Abstract

Monolithic integration of extended short-wave infrared photodetectors (PDs) on silicon is highly sought-after to implement manufacturable, cost-effective sensing and imaging technologies. With this perspective, GeSn PIN PDs have been the subject of extensive investigations because of their bandgap tunability and silicon compatibility. However, due to growth defects, these PDs suffer a relatively high dark current density as compared to commercial III–V PDs. Herein, we elucidate the mechanisms governing the dark current in 2.6 μm GeSn PDs at a Sn content of 10 at. %. It was found that in the temperature range of 293–363 K and at low bias, the diffusion and Shockley–Read–Hall (SRH) leakage mechanisms dominate the dark current in small diameter (20 μm) devices, while combined SRH and trap assisted tunneling (TAT) leakage mechanisms are prominent in larger diameter (160 μm) devices. However, at high reverse bias, the TAT leakage mechanism becomes dominant regardless of the operating temperature and device size. The effective non-radiative carrier lifetime in these devices was found to reach ∼100–150 ps at low bias. Owing to TAT leakage current, however, this lifetime reduces progressively as the bias increases.