Berlin 2005 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 44: II-VI Halbleiter IV
HL 44.1: Vortrag
Montag, 7. März 2005, 15:00–15:15, TU P-N201
Photoreflectance spectroscopy of high-quality ZnO — •H. Lösch1, R. Goldhahn1, G. Gobsch1, A. Dadgar2, N. Oleynik2, J. Bläsing2, and A. Krost2 — 1Institut f. Physik, TU Ilmenau — 2Institut f. exp. Physik, Otto-von-Guericke Universität Magdeburg
We study the influence of preparation conditions on the optical properties of ZnO as determined by temperature-dependent photoreflectance (PR) spectroscopy. The epitaxial layers were grown by MOVPE on GaN/sapphire templates by a two-step growth process. First, a low-temperature ZnO buffer was deposited at 450 ∘C. Then, a high-temperature ZnO layer was grown at 900 ∘C. For doping with nitrogen, unsymmetrical-dimethyl-hydrazine with different molar flows were applied. Generally, doping results in a strongly enhanced magnitude of the PR spectra compared to unintentionally doped films. A further decrease of the line width for the free excitonic transitions is found if moderately doped layers are post-growth annealed in an oxygen atmosphere. Values of about 6 meV at low temperatures confirm the excellent film quality. The fit of the PR spectra for the c-axis layers yields a energetic splitting of 14 meV between the A- and B-excitons. The found lower transition probability of the A-exciton is in agreement with the calculations presented by Gil (PRB 64 (2001) 201301).