GeSn‐on‐Si Avalanche Photodiodes with High Responsivity and Low Dark Current

Abstract GeSn‐on‐Si avalanche photodiodes (APDs) are emerging as a promising solution for low‐light detection in the short‐wave infrared (SWIR) spectral range, including applications in imaging and telecommunications. In this work, key challenges such as high dark current and limited responsivity are addressed by demonstrating devices, which combine low noise with high signal amplification, while remaining compatible with silicon‐based technology. GeSn‐on‐Si APDs with various Sn concentrations up to 1.9% are fabricated and characterized. The GeSn layers are grown pseudomorphically on Ge virtual substrates on Si wafers using molecular beam epitaxy. The devices comprise a double‐mesa structure and exhibit a dark current dominated by a perimeter leakage path, independent of the Sn content. A dark current below 1 µA is maintained up to the onset of avalanche breakdown, marking a significant improvement compared to prior work. A record‐high responsivity of 14.7 A W −1 is achieved at 1550 nm for the APD with 1.9% Sn. Through impulse response measurements, the 3‐dB bandwidth is determined to 1.2 GHz on devices with an 80 µm diameter, resulting in a responsivity‐bandwidth‐product of 17.6 A W −1 GHz −1 . These results highlight the potential of GeSn‐on‐Si APDs for high‐performance, low‐light applications in the SWIR range.