Bond Length Relaxation in Ultrathin InAs and InP0.4As0.6 Layers on InP(001)

Abstract
Bond length relaxation in InAs and InP0.4As0.6 ultrathin layers on InP(001) substrates has been studied by the extended X-ray absorption fine structure using synchrotron radiation. The In–As bond lengths have been determined as a function of film thickness from 1000 Å to 3 Å. In ultrathin film, the In–As bond lengths in both InAs and InP0.4As0.6 alloys are shorter than the bulk value by the epitaxy-induced strain due to the lattice mismatch. It was found that on increasing the film thickness, the In–As bond lengths gradually approach the values in the bulk material. The relative variation of bond length is not dependent on the magnitude of lattice spacing, which suggests that the mechanism of relaxation is ascribed to the local strain (bond length mismatch) rather than the macroscopic average.