Dresden 2011 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 85: Poster Session II
HL 85.121: Poster
Donnerstag, 17. März 2011, 18:00–21:00, P4
Optical investigation on the valence band structure of AlGaN with low Al content — •Tobias Meisch1, Frank Lipski2, Kamran Forghani2, Benjamin Neuschl1, Martin Feneberg3, Ferdinand Scholz2, and Klaus Thonke1 — 1Institut of Quantum Matter, Ulm University, 89069 Ulm, Germany — 2Institut of Optoelectronics, Ulm University, 89069 Ulm, Germany — 3Institut für Experimentelle Physik, Abt. Materialphysik,Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg
For the binary semiconductors GaN and AlN, the crystal field splitting determining the valence band structure changes from ≈ +20 meV (GaN) to ≈ -200 meV (AlN), whereas the spin orbit splitting should remain constant at ≈ 20 meV. Therefore, for unstrained AlGaN ternary layers an interchange of the character of the topmost valence band from Γ9 to Γ7 is theoretically expected for an Al content in the range of 5-10%, manifesting itself mainly in a change of polarization of optical transitions. Strain in epitaxial layers alters the situation and shifts this crossing point. Literature reports experimental values ranging from 20% to 75% Al for the crossover. We present results of temperature dependent photoluminescence and reflectivity experiments on AlGaN layers with Al content ranging from 0 to 30%, and find different contributions from free and bound excitons. The Al content and strain were determined from multiple HRXRD reflections, and entered in a 6x6 k·p model calculation. We discuss our experimental spectra on the basis of this calculation.