Ultrathin low temperature Si0.75Ge0.25/Si buffer layer for the growth of high quality Ge epilayer on Si (100) by RPCVD

Abstract

An approach to grow high quality strain-relaxed Ge by reduced pressure chemical vapor deposition system has been proposed in this paper. Prior to epitaxial growth high quality Ge layer, an ultrathin Si0.75Ge0.25/Si superlattice buffer layer with thickness of 54nm and a 460nm Ge seed layer were deposited successively at low temperature. Then an 840nm thickness Ge layer was grown at high temperature for faster deposition rate. After achieving high-temperature annealing at hydrogen atmosphere, the root-mean-square roughness of the epitaxial Ge lowers to 0.61nm at 10×10μm2 scan area, and the threading dislocation density is 1×106cm−2. Micro-Raman spectra manifests the extremely uniform distribution of tensile strain in Ge layer at room temperature, which can be contributed to the higher thermal expansion coefficient of Ge than that of Si. In contrast to the epitaxial Ge sample without buffer layer, the crystal quality and Hall hole mobility of the Ge epilayer incorporated ultrathin Si0.75Ge0.25/Si buffer improve significantly, indicating that the ultrathin low temperature Si0.75Ge0.25/Si superlattice buffer layer plays an important role on fabricating high quality Ge epilayer.