Low-Misfit Epilayer Analyses using in Situ Wafer Curvature Measurements

Several benefits of in situ wafer curvature monitoring on simple structures with low misfit are discussed. The misfit of lattice-mismatched layers is measured during pseudomorphic growth, allowing for experiments that test relationships between misfit and growth conditions. As an example, Bi incorporation in GaAs is quantified by varying the substrate temperature throughout growth while using curvature measurements to continuously calculate the composition. Results agree well with x-ray diffraction measurements on individual GaAsBi samples, demonstrating the utility of this technique for the study of incorporation in mismatched systems. Once relaxation begins, the strain and dislocation energetics of low-misfit epilayers are determined from changes in wafer curvature. The authors perform several analyses on GaInAs epilayers with different misfits using an anisotropic thin film approximation. Substantial information on dislocation formation and motion is derived from the wafer curvature. Potential applications of this technique include the study of devices that utilize coherently strained layers and structures that intentionally use dislocations to relieve strain. Wafer curvature is a powerful method for comparing strain evolution in mismatched materials.