Vibrational mode and dielectric function spectra of BGaP probed by Raman scattering and spectroscopic ellipsometry

Abstract

The influence of boron incorporation in BxGa1−xP (0 < x ≤ 6%) layers on the dielectric function spectrum and on the vibrational mode spectrum has been studied. BGaP layers were grown by metal-organic vapor phase epitaxy, using a GaP interlayer, on Si and, for reference purposes, also on GaP substrates. The boron content of the layers was determined by high-resolution x-ray diffraction. Two vibrational modes arising from the two boron isotopes 10BGa and 11BGa were observed in the Raman spectrum, increasing in scattering strength and shifting to higher frequencies with increasing boron content at a rate of (1.40 ± 0.20) cm−1/% and (1.41 ± 0.14) cm−1/% for the 10BGa and 11BGa modes, respectively. Spectroscopic ellipsometry was used to asses the pseudodielectric function of the BxGa1−xP layers. The main effect of boron incorporation is a strong broadening of the E1 interband transition with increasing boron content due to alloy disorder and inhomogeneous random strains introduced by the large size mismatch of boron. However, upon the addition of arsenic to BGaP, i.e., forming BxGa1−xAsyP1−y with y ≈ 10%, a clear low-energy shift of the E1 interband transition is resolved. A small low-energy shift (≈ 20 meV) of the lowest direct bandgap has also been observed for BxGa1−xP layers with x ≤ 0.7% grown on GaP substrates.