Theoretical Achievement of THz Gain-Bandwidth Product of Wafer-Bonded InGaAs/Si Avalanche Photodiodes With Poly-Si Bonding Layer

The combination of high-absorption indium gallium arsenide (InGaAs) with Si material (excellent avalanche characteristic) is an ideal solution for the achievement of high-gain low-noise near-infrared avalanche photodetector (APD). Traditional Si-based epitaxial InGaAs thin film suffers from high threading dislocations (TDs), leading to deterioration of noise and gain-bandwidth product (GBP) of APD. InGaAs/Si APD with GBP exceeding terahertz (THz) is reported for the first time theoretically in this work. The calculated APD is based on the semiconductor interlayer bonding in which a thin polycrystalline Si (poly-Si) bonding layer is inserted at the bonded interface to isolate the mismatched lattices of InGaAs and Si single crystals. Extreme low dark current of 10
⁻¹²
A of APD at room temperature is achieved due to the absence of TDs in InGaAs layer and it is located at 10
⁻⁵
A near breakdown voltage (
${V}_{\text{br}}$
). More importantly, a deviation of the dark and optical currents near
${V}_{\text{br}}$
due to the trapping effect of holes at InGaAs/Si bonded interface is identified. The change in gain with bias is inconsistent with the 3-dB bandwidth (BW). The 3-dB BW becomes linear versus bias with the increase in poly-Si thickness, leading to high 3-dB BW (8–10 GHz) near
${V}_{\text{br}}$
. Finally, ultrahigh GBPs of 1.2 and 1.3 THz are achieved for APD with 3- and 5-nm-thick poly-Si bonding layer, respectively. This may give guidance for the fabrication of semiconductor APDs which can meet next-generation high bit-rate applications.