The effect of Si doping upon the structural quality of wurtzite GaN layers which were grown, using molecular beam epitaxy, onto AlN-buffered (111)Si substrates was studied. The planar defect density in the grown GaN layer increased strongly with Si doping. The dislocation density at the free surface of GaN decreased significantly when the Si doping exceeded a limiting value. The Si doping affected the misorientation of the sub-grains that constituted the mosaic structure of GaN. The increase in the planar defect density, and of the out-of-plane misorientation angles of the GaN sub-grains, with Si doping, explained a decrease in the number of dislocations that reached the free GaN surface. A red-shift of the photoluminescence spectra, together with a decrease in the c-axis lattice parameter, with increasing Si doping, reflected an increase in the residual biaxial tensile strain in the GaN samples.

The Effect of Si Doping on the Defect Structure of GaN/AlN/Si(111). S.I.Molina, A.M.Sánchez, F.J.Pacheco, R.García, M.A.Sánchez-García, F.J.Sánchez, E.Calleja: Applied Physics Letters, 1999, 74[22], 3362-4