Observation of strain field fluctuation in SiGe-relaxed buffer layers and its influence on overgrown structures

We investigated in-plane strain field distribution in strained-Si/strain-relaxed SiGe buffer layers by spatially resolved micro-Raman spectroscopy. Crosshatch-like strain distribution was observed in both the strained-Si and SiGe layer, indicating that strain field coming from underlying misfit dislocations reaches the SiGe surface and causes the strain fluctuation in the strained-Si layer. The wavelength of the distribution was found to strongly depend on the SiGe thickness. The amount of the fluctuation corresponded to 13% of the strain that strained-Si layer inherently had. It was also found that the strain field modulated the local growth rate of overgrown layer and caused the enhancement of the surface roughness. The strain fluctuation, therefore, should be carefully taken into account for device applications.