Optical functions, phonon properties, and composition of InGaAsN single layers derived from far- and near-infrared spectroscopic ellipsometry

Abstract

We study the optical properties of compressively strained InxGa1−xAs1−yNy (x<0.13, y<0.03) single layers for photon energies from 0.75 to 1.3 eV (near infrared), and for wave numbers from 100 to 600 cm−1 (far infrared) using spectroscopic ellipsometry. The intentionally undoped InGaAsN 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 InGaAsN for both spectral ranges studied here. The InGaAsN 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 polar strength f of the GaN sublattice resonance changes with nitrogen composition y and with the biaxial strain εxx resulting from the lattice mismatch between InGaAsN and GaAs. This effect is used to derive the nitrogen and indium content of the InGaAsN layers combining the observed f dependence with results from high-resolution double-crystal x-ray diffractometry and using Vegard’s law for the lattice constants and the elastic coefficients C11 and C12. The calculated nitrogen concentrations reflect growth properties such as increasing N incorporation in InGaAsN with decreasing growth temperature, with increasing concentration of nitrogen in the gas phase, and with decreasing indium concentration in InGaAsN.