Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 24: GaN: Pr
äparation und Charakterisierung I
HL 24.12: Vortrag
Dienstag, 25. März 2003, 18:00–18:15, BEY/118
Dielectric Function of "Narrow" Band Gap InN — •Rüdiger Goldhahn1, S. Shokhovets1, V. Cimalla2, O. Ambacher2, J. Furthmüller3, F. Bechstedt3, H. Lu4 und W.J. Schaff4 — 1Institut of Physics, TU Ilmenau, PF 100565, 98684 Ilmenau — 2Center for Micro- and Nanotechnologies, TU Ilmenau — 3FSU Jena — 4Cornell University, Ithaca, U.S.A.
Early studies of sputtered layers indicated a fundamental band gap for InN of about 2 eV. However, recent investigations of MBE grown films revealed a considerably narrower gap of InN between 0.7 eV and 0.9 eV. So far, no reliable experimental data have been reported on the dielectric function (DF) of InN allowing in addition the determination of transition energies for critical points of the band structure. We present for the first time a comprehensive study (spectroscopic ellipsometry in the spectral region of 0.75 eV to 5.5 eV, HRXRD) of MBE grown and sputtered InN films. Only MBE grown layers (band gap 0.8 eV) exhibit a DF coinciding in the spectral dependency with results of first-principles calculations. Two critical points of the band structure are clearly resolved at 4.9 eV and 5.3 eV. In contrast, optical spectra of sputtered InN films show an absorption edge at about 2 eV and a less pronounced structure at higher photon energies. In addition, we present DFs of In-rich InGaN alloys. From the extracted gap energies, a bowing parameter of b=1.5 eV for this alloy system can be estimated. All results provide further evidence that InN is a narrow band gap semiconductor.