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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 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.