Lattice-mismatch-strain effects on excitons in GaAs1-xNx/GaAs heterostructures

We have investigated the lattice-mismatch-strain effect on excitons in GaAs1-xNx (500 nm)/GaAs heterostructures with x = 0.4, 0.8, and 1.5% grown on a GaAs substrate using photoreflectance spectroscopy that is sensitive to excitonic transitions. It is found that the heavy-hole (HH) and light-hole (LH) excitons of the GaAs1-xNx layer, which are degenerate in a bulk crystal, are split and that the energy of the LH exciton is lower than that of the HH exciton, In this case, a quantum-size effect is negligible because the GaAs1-xNx layer thickness is sufficiently thick. The HH-LH splitting energy increases with an increase of nitrogen concentration (x) in addition to a drastic decrease of the energies of the HH and LH excitons. We have quantitatively analyzed the nitrogen-concentration dependence of the energies of the HH and LH excitons, taking account of the lattice-mismatch-strain effect on the band structure and nitrogen-induced giant bowing of the band-gap energy. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim