Development of high-performance short-wave infrared Ge-on-Si linear mode avalanche photodiodes

Short-wave infrared (SWIR) light offers several advantages over visible light, including high eye-safety threshold, reduced atmospheric transmission attenuation, and lower solar background interference. These properties make SWIR light valuable in various applications, such as in optical communications, imaging technologies and automotive industry. Avalanche photodiodes (APDs) are particularly suited for detecting low levels of light due to their internal avalanche gain. Silicon (Si) is favoured as an avalanche material because of its low excess avalanche noise, while germanium (Ge) is an excellent candidate for detecting SWIR light. The use of cost-effective CMOS process technology and the potential for integration with existing Si photonics further enhance the appeal of this material system. Our previous work demonstrated a 50<i>&mu;</i>m-diameter Ge-on-Si linear-mode APD with high avalanche gain and low excess noise at 1550nm wavelength and at room temperature. However, a high dark current still remains one of the main challenges. In this paper, we will present the ongoing development of SWIR Ge-on-Si APDs, focusing on reducing the device dark current by reducing device active area and extending device operating wavelength by employing GeSn as photon absorption region. A 10<i>&mu;</i>m-diameter Ge-on-Si APD shows 8 times dark current reduction at room temperature c.f. the 50<i>&mu;</i>m-diameter Ge-on-Si APD. Furthermore, we designed and fabricated GeSn-on-Si photodiodes with a GeSn thickness of 1<i>&mu;</i>m to investigate device spectrum response at different temperatures.