The effect of Si-doping upon the structural properties of GaN epilayers was investigated for concentrations ranging from 1018 to 8 x 1019/cm3. It was found that the Si-doping changed the stress relaxation mechanism in GaN epilayers on Al2O3 substrates. It reduced the biaxial compressive stress in the layer, as well as changing the domain sizes in the columnar structure, and the densities of both micro-pipes and of vertical screw and edge dislocations along the c-axis. At the same time, the density of misfit dislocations parallel to the interface increased.

Effect of Si Doping on Structural, Photoluminescence and Electric Properties of GaN. N.M.Shmidt, A.V.Lebedev, W.V.Lundin, B.V.Pushnyi, V.V.Ratnikov, T.V.Shubina, A.A.Tsatsulnikov, A.S.Usikov, G.Pozina, B.Monemar: Materials Science and Engineering B, 1999, 59[1-3],195-7