Stress relaxation in thick-film GaN grown by hydride vapor phase epitaxy on sapphire and spinel substrates as studied by photoluminescence and Raman spectroscopy

Abstract

The residual strains in thick-film GaN grown on both sapphire and spinel substrates has been evaluated by photoluminescence (PL) and Raman spectroscopy. The strain-free shallow donor bound exciton recombination energy (I-2) is 3.468 eV at 10 K. The Raman mode frequency shift with residual strain is estimated as Delta omega=3.93 cm(-1) per one GPa for GaN layers on both sapphire and spinel substrate. The strain relaxation is identical for the GaN layers on both substrates. The linear relationship between the PL I-2 line and the Raman E-2 mode frequency is Delta E/Delta omega=5.12 meV/cm(-1) which leads to a stress-induced PL line shift of Delta E=20 meV/GPa.