Intrinsic optical properties of GaN epilayers grown on SiC substrates: Effect of the built-in strain

Intrinsic excitonic properties of GaN/SiC epilayers are studied by photoluminescence and reflectance spectroscopies. The residual built-in tensional biaxial strain, induced by the SiC substrate, is suggested to be responsible for the observed downshift of the excitonic band gap and the reduced valence band splitting in comparison with bulk strain-free GaN samples. By comparing the temperature dependence of the free exciton transition energies for bulk GaN, GaN/SiC, and GaN/Al2O3 samples, residual stress is shown to affect the temperature dependence of the excitonic band-gap energy. (C) 1996 American Institute of Physics.