Near-band-edge photoluminescence and reflection spectra were investigated in GaN grown on Si and Al2O3 substrates. It was found that the doping of GaN both with Si and Mg reduced the value of compressive strain in GaN/Al2O3. In GaN/Si, no evidences of the crossover of A and B excitonic resonance positions with increasing tensile strain was observed. Calculations made by using the non-empirical SCF MO LCAO method showed that the SiGa impurity may lead to an increase of the effective c/a lattice constant ratio, while SiN having greater formation energy produced a lattice relaxation which does not change the c/a ratio significantly. These results were in agreement with experimental observations of decreasing compressive strain in GaN:Si/Al2O3 and increasing tensile strain up to the cracking in GaN:Si/Si.

Luminescence Properties of Strained GaN Epilayers and Spatial Configurations of Silicon Impurity and Related Defects. A.L.Gurskii, E.V.Lutsenko, V.M.Zelenkovskii, T.V.Bezjazychnaja, V.N.Pavlovskii, V.Z.Zubialevich, B.Schineller, O.Schön, G.P.Yablonskii, M.Heuken: Physica Status Solidi C, 2003, 0[1], 425-9