POLARIZED-CATHODOLUMINESCENCE STUDY OF STRESS FOR GAAS GROWN SELECTIVELY ON PATTERNED SI(100)

The spatial variation of stress tensor in selective-area metalorganic chemical-vapor-deposition-grown GaAs on Si substrate by using a linearly polarized cathodoluminescence (CL) technique has been examined. The polarized CL technique enables a precise determination of the energy positions for the strain-split j = 3/2 valence-band excitonic contributions to the luminescence by a simultaneous deconvolution of two CL spectra that are each taken under different polarization detection conditions; this procedure enables a mapping of the stress tensor. The biaxial in-plane stress (sigma(parallel-to) = sigma(perpendicular-to); where parallel-to and perpendicular-to denote parallel and perpendicular, respectively, to a [110]-oriented mesa edge) is found to decrease from approximately 2.2 to 0.5 kbar as the square pattern size is decreased from 1 mm to 10 mum. Patterns having smaller dimension are found to have an increased luminescence efficiency, indicating a reduction in thermal stress induced dislocation density. The stress decay in the vicinity of edges and corners is found to be modeled well with a bimetal thin-film model, showing an approximately exponential decay in stress. A residual tensile stress (comprised of nonzero sigma(perpendicular-to), shear and peeling stress terms) of 0.5-1.0 kbar is found to exist at the edges and corners of the square GaAs mesas; this result agrees qualitatively with an clastic finite-element analysis. The CL results show that the decay length of stress relief near a pattern edge essentially increases with increasing mesa size. The maximum biaxial stress and residual stress near the mesa edges and corners is found to increase with increasing pattern size. Polarized CL imaging is observed to be sensitive to local deviations from biaxial stress and can be used to map the boundaries of stress contours near mesa edges and defects.