Characteristics of InGaPN/GaAs heterostructures investigated by photoreflectance spectroscopy

Photoreflectance (PR) spectra at various temperatures and photoluminescence (PL) spectra and high-resolution x-ray rocking curve (XRC) measurements are used to investigate the band alignment, epitaxial-strain, and atomic-ordering effects in In0.54 Ga0.46 P1-y Ny GaAs (y=0%-2.0%) heterostructures. The existence of additional peaks in PR spectra at higher levels of nitrogen (N) incorporation implies that the band alignment switches from type I to type II, due to the lowering of the conduction band. The electric field at the interface is determined and is discussed with the N content. Redshifts of the PR and PL peaks indicate that the band gap of InGaPN is dramatically reduced as N is incorporated. The valence-band splitting (VBS) and the spin-orbit splitting of InGaPN are obtained from PR spectra. High-resolution XRC measurements indicate that as the N content increases, the lattice mismatch and the compressive strain between the epilayer and GaAs substrate decrease while the VBS increases, which implies an increase in the degree of ordering in InGaPN caused by the transition from a cubic zinc blende structure to a [111] CuPt structure. The order parameter of InGaPN deduced from the VBS ranges from 0.256 to 0.498, indicating that the InGaPN epilayer becomes more ordered with increasing N incorporation.