Investigation of SiNx: Surface passivation impact on InAsP/InGaAs e-SWIR photodiodes

Abstract

In this study, we investigate the deposition of SiNx:H thin films using the inductively coupled plasma chemical vapor deposition (ICPCVD) method with NH3/SiH4 ratios ranging from 1.3 to 25. The impacts of these variations on extended short-wave infrared region (e-SWIR) photodiodes (PDs) were characterized through stress, reflectance, photoresponse, and dark current modeling techniques. It was observed that an increase in H content leads to a decrease in both the refractive index and stress. To reveal the effects of H content on the bond numbers of N-H, Si-H, and Si-N within SiNx:H, FTIR measurements were conducted. This allowed us to investigate the K − trap centers depending on the change in NH3/SiH4 ratios. The influence of H content on the passivation layer was examined through dark current modeling and PD performance evaluations. The optimized passivation layer underscores that the dark current of the PD is G-R limited, with diffusion current emerging as the dominant component at high temperatures. Additionally, the PD performance was enhanced with optimized passivation, achieving a higher photo-to-dark current ratio, a responsivity of 0.97 A/W at $2~\mu$ m, an external quantum efficiency (E.Q.E.) peak of 70.8% at $1.6~\mu$ m, and a dark current density of $120~\mu$ A/cm2 at 300 K under a 100 mV reverse bias voltage.