Local structure in semiconductor superlattices and epilayers

We report XAFS studies of two related strained semiconductor systems: nominally matched short period InGaAs/InP(001) superlattices and strained epilayers of InxGa1-xAs on InP(001). In InGaAs/InP superlattices coordination numbers deviate significantly from the abrupt interface case, demonstrating the presence of strained interface layers. This provides a local structural explanation for the non-negligible average lattice mismatch measured by diffraction. The analysis of strained epilayers of InxGa1-xAs/InP(001) allows us to study in detail bond lengths in strained semiconductors. We demonstrate that, notwithstanding the rigidity of semiconductor bonds, strain induces variations of nearest neighbor distances: bond lengths can be stretched or compressed. A model which reproduces strain-induced variations is presented.