Optical phonon modes and interband transitions in cubic (formula presented) films

A. Kasic, M. Schubert, T. Frey, U. Köhler, D. J. As, C. M. Herzinger

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


We present a comprehensive study of the phonon mode behavior and the optical interband transitions of cubic (formula presented) films (formula presented) using spectroscopic ellipsometry from the midinfrared to the vacuum-ultraviolet spectral range (0.05-8.5 eV). The (formula presented) layers were grown by radio-frequency plasma-assisted molecular-beam epitaxy and possess free-electron concentrations in the range of (formula presented) A two-mode behavior for the transverse-optical phonon of (formula presented) is observed, which is consistent with theoretical predictions. Due to the high free-electron concentration, the observed (formula presented) fundamental band-gap energy (formula presented) is subject to a strong Burstein-Moss shift and band-gap renormalization. We quantify the amount of both band-gap shifting mechanisms, and provide an estimate for the composition dependence of the (formula presented) band-gap energy (formula presented) which depends approximately linearly on the alloy composition with (formula presented) at room temperature and for carrier-depleted material. For cubic GaN, the L-point interband transition (formula presented) shifts to lower energies with increasing free-electron concentration, whereas the interband transition (formula presented) remains unshifted. Increasing Al content induces a blueshift (redshift) of the (formula presented) for (formula presented) Due to strong broadening effects, both transitions cannot be differentiated anymore for (formula presented).

Original languageEnglish (US)
Pages (from-to)1-13
Number of pages13
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number18
StatePublished - 2002
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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