Luminescence Properties of Strained GaN Epilayers and Spatial Configurations of Silicon Impurity and Related Defects

Near-band-edge photoluminescence and reflection spectra have been investigated in GaN grown on Si and Al2O3 substrates. It has been found that the doping of GaN both with Si and Mg reduces 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. The calculations 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 produces a lattice relaxation which does not change the c/a ratio significantly. These results are 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.