Comparison of SiNx-Based Surface Passivation Between Germanium and Silicon

Abstract

Germanium (Ge) has attracted much attention as a promising channel material in nanoscale metal–oxide–semiconductor devices and near-infrared sensing because of its high carrier mobilities and narrow bandgap, respectively. However, efficient passivation of Ge surfaces has remained challenging. Herein, silicon nitride (SiNx)-based passivation schemes on Ge surfaces are studied and the observations are compared to Si counterparts. These results show that instead of a high positive charge density (Qtot) that is found in SiNx-passivated Si samples, similar Ge samples contain a high amount of negative Qtot (in the range of 1012cm−2). The maximum surface recombination velocity of the samples is shown to reduce by a factor of three in both Si and Ge samples by a post-deposition anneal at 400 °C. The SiNx-coated samples are capped with an atomic-layer-deposited aluminum oxide (Al2O3) layer, which reduces the midgap interface defect density (Dit) after annealing to 7 × 1010 and 4 × 1011 cm−2 eV−1 in Si and Ge, respectively. Interestingly, while the Al2O3 capping seems to have no impact on Qtot of the Si samples, it turns the stack virtually neutral (∼−1.6 × 1011 cm−2) on Ge. The presented SiNx-based passivation schemes are promising for optoelectronic devices, where a low Dit and/or a low charge are favored.