Dresden 2014 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 53: Nitrides: Preparation of nonpolar and semipolar orientations
HL 53.8: Talk
Tuesday, April 1, 2014, 15:45–16:00, POT 151
Generalized ellipsometry of semipolar AlGaN — •Juliane Klamser1, Martin Feneberg1, Rüdiger Goldhahn1, Joachim Stellmach2, Martin Frentrup2, Simon Ploch2, Frank Mehnke2, Tim Wernicke2, and Michael Kneissl2 — 1Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg — 2Institut für Festkörperphysik, Technische Universität Berlin
We present generalized spectroscopic ellipsometry data obtained from the anisotropic semiconductor material system aluminum gallium ni- tride (AlGaN). The several micrometer thick AlGaN layers were grown by metal-organic vapor phase epitaxy on m-plane sapphire substrates. The samples cover the whole composition range between GaN and AlN. The (11-22) orientation of the AlGaN surface allows for alignment of the optical axis parallel to the plane of incidence, no perpendicular alignment is possible. The optical axis of the as well anisotropic sapphire substrate is pointing in a different direction. This challenging sample geometry requires careful measurement of the main and the secondary elements of the Jones matrix. As result of the evaluation of the measurements we present the successfully separated ordinary and extraordinary tensor components of the dielectric function. We not only succeeded in fitting model dielectric functions to experimental data but also present point-by-point fitted dielectric functions of several AlGaN samples. The valence band structure of AlGaN governing optical selection rules and thus the dielectric function is expected to show a crossing at certain but unknown Al concentration. Our study experimentally narrows the possible band crossing range in AlGaN.