Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 27: GaN: Pr
äparation und Charakterisierung
HL 27.7: Vortrag
Mittwoch, 10. März 2004, 16:45–17:00, H15
Chemically ordered AlxGa1−xN alloys: Spontaneous formation of natural quantum wells — •L. Lymperakis1, M. Albrecht2, J. Neugebauer1,3, J.E. Northrup4, L. Kirste5, and H.P. Strunk2 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin — 2Universität Erlangen-Nürnberg, Lehrstuhl Mikrocharakterisierung — 3Universität Paderborn — 4Palo Alto Research Center, CA 94304, U.S.A. — 5Freiburger Materialforschungszentrum, Universität Freiburg
We have combined density-functional theory (DFT) calculations with x-ray and transmission electron microscopy experiments to study formation, stability, and structural and optical properties of ordered AlxGa1−xN. Our calculations show that ordered structures are thermodynamically unstable against disorder. We have therefore explored whether kinetics may be used to achieve ordering. Based on our calculations we find that adatom kinetics at surface steps can induce ordering. An analysis of the computed electronic structure showed that ordering significantly affects the electronic structure: it causes a redshift in the band gap by 100 meV. The theoretical predictions have been confirmed by the experimental studies. Under appropriate growth conditions an alternating 1×1 AIN/GaN superlattice forms. While transmission electron microscopy shows the presence of ordered domains, annealing under high pressure and high temperature leads to disappearance of the superlattice, accompanied by a blue shift of the luminescence up to 140 meV.