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HL: Fachverband Halbleiterphysik

HL 51: GaN: preparation and characterization

HL 51.7: Talk

Friday, March 30, 2007, 12:30–12:45, H13

Band gap and Van-Hove singularities of cubic InN — •Pascal Schley¹, Rüdiger Goldhahn¹, Christian Napierala¹, Gerhard Gobsch¹, Jörg Schörmann², Donat J. As², Klaus Lischka², Frank Fuchs³, and Friedhelm Bechstedt³ — ¹Institut für Physik, TU Ilmenau — ²Department Physics, Universität Paderborn — ³Institut für Festkörpertheorie und -optik, FSU Jena

InN has attracted much interest recently due to the band gap revision for the hexagonal compound from the long-time accepted value of 1.89 eV down to only 0.68 eV. Theoretical calculations predict an even lower gap for the cubic (c-) counterpart. We succeeded in growing single crystalline c-InN films on 3C-SiC substrate with a c-GaN buffer layer by MBE. Ellipsometry was applied in order to determine the dielectric function (DF) of c-InN from the near infrared into the VUV spectral region (data above 4 eV refer to the use of synchrotron radiation at BESSY II). The spectra show pronounced features in the high-energy part which arise from the Van-Hove singularities in the band structure. High-resolution transition energy determination is achieved by fitting the third derivatives of the DF. The values as well as the shape of the DF are in excellent agreement with the results of DFT-LDA calculations for which electron-hole interaction was taken into account. The position of the absorption edge depends clearly on the electron density of the films. Taking into account carrier-induced band gap renormalization and the Burstein-Moss shift we estimate the zero-density band gap of c-InN with 0.62 eV which is by 60 meV lower than for hexagonal InN.