Microcrystalline Ge interlayer-bonded InGaAs/Si avalanche photodiode with ultrahigh responsivity of 135 A/W and gain of 190

This paper reports a high-performance InGaAs/Si avalanche photodiode (APD) utilizing a microcrystalline germanium (μc-Ge) interlayer bonding technique. This technique enables the formation of a high-quality InGaAs/Si heterojunction with a void-free, high-strength, and oxide-free bonded interface, effectively suppressing dislocation formation and elemental interdiffusion. The device demonstrates high responsivities of 68 A/W and 135 A/W at wavelengths of 1310 nm and 1550 nm, respectively, with avalanche gains of 106.25 and 190, respectively, significantly outperforming previously reported Ge/Si and various InGaAs-based APDs. Further observation shows that the punch-through voltage increases with rising optical power, attributed to the space charge effect caused by the hole potential well at the μc-Ge bonded interface. Additionally, a defect-assisted tunneling mechanism for interfacial carrier transport is revealed. This work presents an effective technological pathway for the development of high-performance, low-noise III-V/Si integrated photodetectors.