TY - JOUR
T1 - Optical phonon modes and interband transitions in cubic (formula presented) films
AU - Kasic, A.
AU - Schubert, M.
AU - Frey, T.
AU - Köhler, U.
AU - As, D. J.
AU - Herzinger, C. M.
PY - 2002
Y1 - 2002
N2 - 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).
AB - 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).
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U2 - 10.1103/PhysRevB.65.184302
DO - 10.1103/PhysRevB.65.184302
M3 - Article
AN - SCOPUS:85038300683
VL - 65
SP - 1
EP - 13
JO - Physical Review B-Condensed Matter
JF - Physical Review B-Condensed Matter
SN - 1098-0121
IS - 18
ER -