Vibrational mode and dielectric function spectra of BGaP probed by Raman scattering and spectroscopic ellipsometry $1S. Rogowsky$1M. Baeumler$1M. Wolfer$1L. Kirste$1R. Ostendorf$1J. Wagner$2S. Liebich$2W. Stolz$2K.

摘要

The influence of boron incorporation in BxGa_(1-x)P (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 ~10B_(Ga) and ~11B_(Ga) 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 ~10B_(Ga) and ~11B_(Ga) modes, respectively. Spectroscopic ellipsometry was used to asses the pseudodielectric function of the BxGa_(1-x)P layers. The main effect of boron incorporation is a strong broadening of the E_1 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 BxGa_(1-x)As_yP_(1-y) with y ≈ 10%, a clear low-energy shift of the E_1 interband transition is resolved. A small low-energy shift (≈ 20 meV) of the lowest direct bandgap has also been observed for BxGa_(1-x)P layers with x ≤ 0.7% grown on GaP substrates.