Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 51: Poster IV
HL 51.43: Poster
Thursday, February 28, 2008, 16:30–19:00, Poster D
Empirical pseudopotential calculation of strain induced birefringence in ZnO — Daniel Fritsch1 and •Heidemarie Schmidt2 — 1Leibniz Institute for Solid State and Materials Research IFW Dresden, PO Box 270116, D-01171 Dresden, Germany — 2Forschungszentrum Dresden-Rossendorf e.V., PO Box 510119, D-01314 Dresden, Germany
One big challenge in the fabrication of ZnO-based heterostructure devices is the lattice mismatch between ZnO films and substrates and the different thermal expansion coefficients inducing biaxial strain. There is currently also much interest in ZnO doped with 3d transition metal ions for spintronics applications and the detection of ferromagnetic signatures by magneto-optical measurements of ordering induced birefringence being most intense around the critical point structure of the dielectric function. A quantitative understanding of Zeeman splitting far away from the center of Brillouin zone is still an open question and requires a separation of strain and magnetic field induced modifications of the electronic band structure. We report on the effect of strain on the birefringence in ZnO films grown on Al2O3 or on SiC substrates. The imaginary part of the dielectric function has been calculated by means of the empirical pseudopotential method. Thereby we also accounted for relativistic effects in form of the spin-orbit interaction, for the energy-dependence of the crystal potential through the use of nonlocal model potentials, and for excitonic contributions to the dielectric function due to discrete excitonic states and Coulomb-enhanced band-to-band transitions.