Model dielectric function spectra of GaAsN for far-infrared and near-infrared to ultraviolet wavelengths

We study the optical properties of tensile strained GaAs1-yNy (0%less than or equal toy less than or equal to3.7%) single layers for photon energies from 0.75 to 4.5 eV and for wave numbers from 100 to 600 cm(-1) using spectroscopic ellipsometry. The intentionally undoped GaAsN layers were grown pseudomorphically on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor phase epitaxy. We provide parametric model functions for the dielectric function spectra of GaAsN for both spectral ranges studied here. The model functions for photon energies from 0.75 to 4.5 eV excellently match dielectric function data obtained from a numerical wavelength-by-wavelength inversion of the experimental data (point-by-point fit). Critical-point analysis of the point-by-point fitted dielectric function is performed in the spectral regions of the fundamental band gap and the critical-point transitions E-1 and E-1+Delta (1). The band-gap energy is redshifted whereas the E-1 and E-1+Delta (1) transition energies are blueshifted with increasing y. For y less than or equal to1.65% the observed blueshift of the E-1 energy is well explained by the sum of the effects of biaxial (001) strain and alloying. The GaAsN layers show a two-mode phonon behavior in the spectral range from 100 to 600 cm-1. We detect the transverse GaAs- and GaN-sublattice phonon modes at wave numbers of about 267 and 470 cm(-1), respectively. The oscillator strength of the GaN-sublattice resonance increases linearly due to alloying and tensile strain. We compare our results from the single layers with those obtained previously from tensile and compressively strained GaAsN/GaAs and GaAsN/InAs/GaAs superlattices. (C) 2001 American Institute of Physics.