Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 27: GaN: Pr
äparation und Charakterisierung
HL 27.4: Vortrag
Mittwoch, 10. März 2004, 16:00–16:15, H15
Anisotropy of the Dielectric Function for wurtzite InN — •R. Goldhahn1, A.T. Winzer1, V. Cimalla2, O. Ambacher2, C. Cobet3, N. Esser3, J. Furthmüller4, F. Bechstedt4, H. Lu5, and W.J. Schaff5 — 1Institute of Physics, TU Ilmenau, PF 100565, 98684 Ilmenau — 2Center for Micro- and Nanotechnologies, TU Ilmenau — 3TU Berlin — 4FSU Jena — 5Cornell University, Ithaca, U.S.A.
Theoretical calculations of the dielectric function (DF) for wurtzite InN predict a pronounced anisotropy in the range of the high-energy critical points of the band structure. Neither for MBE/MOVPE grown layers (gap energy ∼ 0.7 eV) nor sputtered films (absorption edge ∼ 1.9 eV) such an anisotropy has been reported yet. We succeeded in growing a-plane InN on r-plane sapphire substrate by plasma-assisted MBE. Those layers offer the advantage that the light can be polarized parallel and perpendicular to the optic axis (c-axis) allowing the direct determination of both the ordinary and extraordinary component of the DF tensor. Here, results of spectroscopic ellipsometry measurements in the energy range from 0.7 up to 9.5 eV (partly using synchrotron radiation) are presented. For the first time, strong optical anisotropy of InN is demonstrated in the energy range above 4.5 eV. The data are compared with results of first-principles band structure and DF calculations. Data analysis in the near band gap range proves in addition a strong non-parabolicity of the conduction band. All results provide further evidence that InN is a narrow band gap semiconductor.