Low-temperature photoluminescence, transmission electron microscopic, X-ray diffraction and Raman spectroscopic studies were made of stress relaxation and dislocation structures in a layer of Si-doped material. The results were compared with those for an undoped layer that had been grown onto Al2O3 by means of metalorganic vapor phase epitaxy. It was found that doping with Si to a concentration of 3 x 1018/cm3 improved the layer quality. It decreased the dislocation density from 5 x 109 in the undoped layer to 7 x 108/cm2, and made the dislocation distribution more random. Both samples were shown to be under a biaxial compressive stress; which was slightly higher in the undoped layer. These stresses resulted in a blue shift of the emission energy and E2 phonon peaks in the photoluminescence and Raman spectra. The thermal stress was partially relaxed by the bending of threading dislocations into the basal plane. This led to the formation of a 3-dimensional dislocation network and to a strain gradient along the c-axis of the layer.

S.Ruvimov, Z.Liliental-Weber, T.Suski, J.W.Ager, J.Washburn, J.Krueger, C.Kisielowski, E.R.Weber, H.Amano, I.Akasaki: Applied Physics Letters, 1996, 69[7], 990-2