Effect of Strained-Si Layer Thickness on Dislocation Distribution and SiGeRelaxation in Thin Buffer Layer Strained-Si/SiGe Heterostructures

摘要

Strained-Si (sSi) on SiGe heterostructures have been prepared by chemicalrnvapor deposition and examined by preferential defect etching and Ramanrnspectroscopy. Defect etching revealed threading dislocations (TDs) in thernsuper-critical thickness sSi samples are more evenly distributed, whilernthey are more trapped inside TD pileups in the sub-critical thickness sSirnsamples. The TD density is in the range of (3~5) x 106 cm-2, which doesrnnot depend on the sSi or SiGe thicknesses. Raman spectroscopy revealedrnthat the relaxation degree of the 300 nm SiGe layer decreases from 80% torn67% with the sSi layer increase from 8 nm to 40 nm, suggesting arncontinuous relaxation of the highly compressively strained, thin SiGernbuffer during or after sSi growth. The 600 nm SiGe buffer has a ～82%rnrelaxation for all sSi thickness, suggesting that the relatively small residualrnstrain cannot support any further relaxation after switching to sSi growth.rnBased on these observation, we suggest that an in-situ thermal annealingrnprior to the sSi growth will help to enhance the strain relaxation of thinrnSiGe buffers.