Effect of Si-Ge interdiffusion on the waveguide properties of SiGe-Si MQW photodetector

Because of Si-Ge interdiffusion in the Si-SiGe interface during the growth process, the square-wave refractive index distribution of a SiGe-Si multiple-quantum-well (MQW) will become smooth. In order to simulate the actual refractive index profile, a staircase approximation is applied. Based on this approach, the dispersion equation of the MQW waveguide is obtained by using a transfer matrix method. The effects of index changes caused by the interdiffusion on the optical field and the characteristics of the photodetector are evaluated by solving the dispersion equation. It is shown that the Si-Ge interdiffusion can result in a reduction of the effective absorption coefficient and the quantum efficiency.