Abstract:
We propose a novel design of Ge1-xSnx-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 multi-dot 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 (NEP) exhibit less sensitivity to variations in Sn concentration. All devices exhibit exceptionally low dark currents (<75 pA), a high GeSn absorption coefficient, and a high triggering probability (>95%), yielding a significant SPDE (>82.2%). Furthermore, the minimal DCR value (< 0.0095 Mcps) combined with a high SPDE results in a low noise equivalent power (< 0.02 fWHz-0.5) and high detectivity at λ = 1.55 μm and VEX = 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).