SILICON-GERMANIUM PHOTODIODE

摘要

When there is a lattice mismatch of approximately 4% between Si and Ge, and when a Ge layer is grown on top of a Si layer, a threading dislocation is introduced, causing a leakage current at the p-i-n junction. As a consequence, the light receiving sensitivity drops, and the reliability of the device decreases. Other issues when connecting to a Si waveguide are reflection loss caused by the refractive index difference between Si and Ge, and absorption loss caused by a metal electrode. In order to resolve these issues, a vertical-type pin-SiGe photodiode is structured so as to be embedded in a groove formed in one part of the Si layer; with a p-type or n-type doped layer formed in the bottom part of the groove; and a rectangular or inverse-tapered i-SiGe formed on top of the layer, and on top of the i-Si layer and Si-Ge buffer layer stacked on the bottom and side walls. Furthermore, for the part that optically connects to the Si waveguide, impedance matching is implemented due to the stacked structure of the i-Si layer and the Si-Ge buffer layer, isolating the upper metal layer and establishing an electrical connection due to a poly-Si bridge structure.