Growth of high quality Ge-on-Si layer by using an ultra-thin LT-Si buffer in RPCVD

Abstract

Ge epitaxial layer on Si substrate becomes more attractive for Si-based monolithic photonic integrated circuit (PIC). Low threading dislocation density and low surface roughness play a vital role in realizing the fabrication of the Ge optoelectronic devices. In this study, an ultra-thin LT-Si buffer for the deposition of Ge layer was investigated with regard to Ge layer’s crystallinity, symmetrical characteristic, threading dislocation density, and surface roughness. As a result, Ge epitaxial film has low threading dislocation density (TDD=5×106cm−2) and smooth surface (RMS = 0.68nm) in 5µm×5µm scan field with the Ge epitaxial layer thickness of about 1µm. What’s more, it was grown in a short time by using an ultra-thin LT-Si buffer layer without using chemical mechanical polishing (CMP), high temperature annealing, H2 annealing or cyclic annealing. In addition, room temperature direct gap photoluminescence was observed from intrinsic tensile-strained (0.21%) Ge-on-Si layer and bandgap narrowing in Ge epitaxial layer is 85meV.