A Trenched Ge-on-Si SPAD With Low Dark Current Utilizing Aspect Ratio Trapping Technology

Ge-on-Si single-photon avalanche diode (SPAD) operating in the short-wave infrared (SWIR) band is particularly advantageous for applications, including quantum key distribution (QKD), 3-D imaging, and biological imaging, owing to its high responsivity and rapid response. Ge is compatible with the mainstream Si complementary metal–oxide–semiconductor (CMOS) process, making Ge-on-Si SPAD highly desirable. However, the large area of the Ge–Si interface and poor quality of Ge epitaxy material grown on Si substrate leads to a large dark current, presenting a significant challenge for applications that demand low noise and high sensitivity. In this work, we have designed and simulated a novel trenched Ge-on-Si heterodevice structure using both Si and Ge layers, employing aspect ratio trapping (ART) and lateral epitaxial overgrowth (LEO) technologies for Ge growth. The unique trench structure design leads to a remarkable reduction in dark count rate (DCR), achieving 0.164 MHz under a 5% excess bias based on our simulation results for a 450-nm-thick absorption layer device. This value is substantially lower than that of the conventional mesa structure, whose smallest DCR is 4.27 MHz, as reported in the literature, and 6.38 MHz in our simulated mesa structure under the same condition. Additionally, our device attained a single-photon detection efficiency (SPDE) of 9.91%. By further increasing the thickness of the absorption layer, a higher SPDE of 17.63% can be achieved. This innovative structural design provides a promising pathway for developing highly sensitive detectors operating at room temperature.