Regensburg 2004 – scientific programme

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HL: Halbleiterphysik

HL 12: Poster I

HL 12.86: Poster

Monday, March 8, 2004, 16:30–19:00, Poster A

Temperature-dependent band-gap energies and optical constants of ZnO — •N. Ashkenov, M. Schubert, W. Chakai, G. Benndorf, H. Hochmuth, M. Lorenz, and M. Grundmann — Fakultät für Physik und Geowissenschaften, Institut für Experimentelle Physik II, Universität Leipzig, Linnéstraße 5, 04103 Leipzig

We report the temperature dependencies of the fundamental band-to-band transition energies and the below-band-gap refractive index in ZnO. Spectroscopic ellipsometry data, taken from a (0001)-cut ZnO single crystal at temperatures between 300 K and 1154 K, and for photon energies from 1.25 eV to 3.335 eV, are analyzed by using model dielectric function approaches, augmented by excitonic continuum contributions. A strong and linear red-shift of the three wurtzite-type Γ-point transition energies is observed. The increase of the valence band splitting energies upon temperature is indicative for an increase of the quasi-cubic model parameters. Results of photoluminescence studies between 4.4 K and 300 K are used to supplement the high-temperature band-gap data. For ZnO, the phonon dispersion must be considered appropriately in order to model the temperature dependence of the fundamental band-to-band transition energy. We obtain strong contributions due to optical phonons at elevated temperatures, whereas acoustic phonons dominate the electron-phonon coupling at low temperatures.