Enhanced surface passivation of predictable quantum efficient detectors by silicon nitride and silicon oxynitride/silicon nitride stack

Abstract

In this paper, we investigate three different passivating films for use in predictable quantum efficient detectors: two monolayer films of SiNx with different compositions and one double-layer stack of SiNxOy capped with SiNx, all deposited on very high resistivity silicon substrates. In addition to the conventional characterization methods, we also utilize the novel method of photoluminescence imaging under applied bias (PL-V) and high voltage soaking to modulate the fixed charge density Qf in the layers. All films exhibit very good passivating properties after deposition and annealing, with the oxynitride stack providing the best passivation, resulting in an effective carrier lifetime close to 20 ms. This value is explained by a relatively high fixed charge density of Qf = 1.12 × 1012 cm−2 and low interface defect density (S0,n = 6.0 × 102 cm/s), giving a chemical passivation which is an order of magnitude better than the investigated nitrides. Both nitride films were readily charged by voltage soaking, increasing the effective carrier lifetime by about 20%. Based on the passivating properties, photodetector device simulations predict that self-induced photodiodes made with any of these passivation layers will have an internal quantum deficiency well below 1 ppm for selected wavelengths at room temperature, and all the investigated materials are thus good candidates for use as passivating layers in such photodiodes.