Misfit stress in InGaAs/InP heteroepitaxial structures grown by vapor-phase epitaxy

Abstract

Misfit stress in InGaAs/InP heteroepitaxial structures grown by hydride-transport vapor phase epitaxy has been studied using an x-ray technique to measure the wafer curvature and using an x-ray double crystal diffractometer to measure mismatches. The stress calculated from the measured radius of curvature was, in all cases, found to be smaller than the value predicted from the lattice mismatch using the simple beam theory and assuming a coherent interface. A simple argument is used to show that the parallel mismatch is directly related to the density of misfit dislocations. By taking into account both the presence of misfit dislocations and tetragonal distortion, relationships between the curvature, density of interfacial misfit dislocations, relaxed lattice mismatch, and measured tetragonally distorted vertical and parallel mismatches are derived. Predicted values for the radius of curvature agree very well with measured values. The results also indicate that in the presence of interfacial misfit dislocations the nature of the stress in the epitaxial layer is not uniquely determined by the mismatch. The stress can change sign depending upon the density of the misfit dislocations. This effect has actually been observed. The defect structure of the epitaxial layer is analyzed by Nomarski interference contrast microscopy, transmission x-ray topography, and transmission electron microscopy. We have found that the misfit stress can be greatly relaxed in the presence of lattice defects such as stacking faults. The theoretical calculation is further generalized from the single epilayer/substrate case to an n-layer heterostructure. The determination of the stresses in each layer and the misfit dislocation densities are discussed.