Piezoreflectance and contactless electroreflectance spectra of an optoelectronic material: GaInNP grown on GaAs substrates

We report a detailed study of piezoreflectance (PzR) and contactless electroreflectance (CER) on Ga_0.44In_0.56N _xP_1-x epitaxial layers at room temperature. The polarized PzR spectra show anisotropic character along the [110] and [11̄0] directions. Ordering-induced superlattice-like microstructure shown in high resolution transmission electron microscope (HTEM) images confirms the spontaneous ordering in Ga_0.44In_0.56N_xP _1-x epitaxial layers. The obtained PzR and CER spectra are fitted with the theoretical line shape functional form. The valence-band maximum, crystal field/strain splitting and spin-orbit splitting to conduction band transition energies denoted as E_g, E_g+Δ ₁₂ and E_g+Δ₁₃, respectively, are accurately determined. With nitrogen incorporation, the PzR and CER features red-shifts, indicating band gap reduction. The experimentally observed band gap energy reduction of GaInP incorporation nitrogen is of the same order as for nitrogen in binaries. However, the bowing coefficient b is determined to be -10.5eV, that is considerable smaller than that of the incorporation of nitrogen in InP (b=-16eV) or GaP (b=-14eV).