Strain state in GaN epilayers from optical experiments

The intrinsic optical properties of GaN thin epilayers grown on a sapphire substrate and by Mg-enhanced lateral overgrowth (ELO) are studied as a func tion of temperature (from 20 up to 250 K) by means of photoluminescence exc itation spectroscopy. The comparison between the experimental and calculate d results allows us to determine the strain state of the GaN layers. At low temperature (T=20 K) the strain is stronger in the ELO epilayers than in t he GaN layers grown on sapphire, but, contrary to the GaN layers grown on t he sapphire substrate, the strain state remains constant in the overgrown G aN layers when temperature varies. (C) 2001 American Institute of Physics.