Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 31: Poster II
HL 31.1: Poster
Dienstag, 26. Februar 2008, 16:30–19:00, Poster D
Temperature dependency of valence and conduction bands studied by means of synchrotron spectroscopic ellipsometry — •Christoph Cobet1, Christoph Werner1, Munise Rakel1, Wolfgang Richter2, and Norbert Esser1 — 1ISAS- Institute for Analytical Sciences, Department Berlin, Albert-Einstein-Str. 9, D-12489 Berlin — 2Dipartimento di Fisica, Roma II (Tor Vergata), Via della Ricerca Scientifica 1, I-00133 Rome, Italy
A common experimental approach to study temperature effects on the electronic band structure is using spectroscopic ellipsometry. Thereby the energy shift and broadening of interband transition features in the dielectric function is determined. A major problem in the interpretation is related to the fact that the observed transitions correspond to pairs of valence and conduction bands i.e. the joint density of states. Therefore, only a sum of the respective contributions is measured. In the presented work we utilize the strongly localized semicore Ga3d states in GaN, which are almost unaffected by the electron-phonon interaction, as an energy reference. Excitations from these Ga3d levels to conduction bands occur in the dielectric function above 20eV. In this spectral range temperature related shifts and broadening of transition features thus only relate to changes in conduction bands. In a critical-point analysis we finally separate temperature effects i.e. electron phonon coupling constants for conduction and valence band states. These experiments can be used as a critical test for existing empirical models and newly developed parameter-free ab-initio calculations.