Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 53: Nitrides: Preparation of nonpolar and semipolar orientations

HL 53.8: Vortrag

Dienstag, 1. April 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 Kneissl21Institut 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.

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