Structural Origin of Optical Bowing in Semiconductor Alloys

The principle of conservation and transferability of chemical bonds explains the recent discovery by extended x-ray-absorption fine-structure measurements of two unequal anion-cation bond lengths $R_{\mathrm{AC}}$ and $R_{\mathrm{BC}}$ in $A_x{B}_{1-x}C$ zinc-blende semiconductor alloys despite the close adherence of the lattice constant to the average value (Végard rule). This bond alternation, manifested as a structural distortion to a local chalcopyrite coordination around the anions, explains also most of the observed optical bowing in semiconductor alloys.