Influences of composition on Raman scattering from GeSi alloy core-shell nanowire heterostructures

In this paper, the influences of composition on Raman scattering from Ge/Si-GeSi core-shell nanowire heterostructures standing along [011] and [111] crystal directions are numerically investigated. Uniform, linear and spontaneous nonlinear composition profiles (CPs) in GeSi alloy shell are taken into consideration. In uniform CP case, clear double peaks in Raman spectra contributed by core and shell are observed. The strain-induced shift follows linear relation with Ge concentration and nonlinear relation with shell thickness. Larger strain-induced shifts are obtained in nanowires along [111] direction. In linear CP case, the peaks contributed by shell cannot be distinguished in the total spectra and plateaus are formed on the low frequency side. Moreover, the nonlinear CP accounts for the spontaneous composition transition near heterointerface during lateral epitaxy of GeSi shell. Due to the rapid Ge concentration transition, Raman spectra are shown nearly identical to uniform CP cases.