A Novel n+/i-Well Dot Ge1−xSnx-on-Si Single-Photon Avalanche Photodiode for High-Fill-Factor Room-Temperature Quantum Applications

Abstract

We propose a novel design of ${{\mathrm{Ge}}_{1 - x}}{{\mathrm{Sn}}_x}$-on-Si single-photon avalanche photodiodes (SPADs) that aim to enhance the fill factor (FF) and minimize noise at room temperature. The device consists of a ${{n}^ + }/i$-well dot structure designed to eliminate the need for guard rings and multidot or array configurations typically used to enhance the active area. This study considers three distinct concentrations of Sn (4%, 6%, and 8%) in the GeSn active layer and investigates their effect on performance metrics. The impact of the threading dislocation density in defective GeSn on the dark count rate (DCR) is also examined. The results show that a high Sn concentration has a notable impact on dark current. However, the DCR, single-photon detection efficiency (SPDE), and noise-equivalent power exhibit less sensitivity to variations in Sn concentration. All devices exhibit exceptionally low dark currents (<75>95%), yielding a significant SPDE (>82.2%). Furthermore, the minimal DCR value (<0.0095>−0.5) and high detectivity at λ = 1.55 μm and ${{V}_{\text{EX}}}$ = 5 V. The GeSn-on-Si SPADs here address the challenges faced by current Ge-on-Si, SiGe, InGaAs/AlGaAsSb, and InGaAs/InP SPADs regarding low operating temperatures, showcasing their promise for quantum photonics and communication applications at room temperature (T = 300 K).