Bond-Length Distortions in Strained Semiconductor Alloys

Extended x-ray absorption fine structure measurements performed at $\mathrm{In}-K$ edge have resolved the outstanding issue of bond-length strain in semiconductor-alloy heterostructures. We determine theIn-As bond length to be $2.581\pm 0.004Å$ in a buried, 213 Å thick ${\mathrm{Ga}}_{0.78}{\mathrm{In}}_{0.22}\mathrm{As}$ layer grown coherently on GaAs(001). This bond length corresponds to a strain-induced contraction of $0.015\pm 0.004Å$ relative to the In-As bond length in bulk ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{As}$ of the same composition; it is consistent with a simple model which assumes a uniform bond-length distortion in the epilayer despite the inequivalent In-As and Ga-As bond lengths.