Contactless electroreflectance spectroscopy of InN layers grown by MBE
M. Motyka, R. Kudrawiec, J. Misiewicz
Institute of Physics, Wrocław University of Technology,
Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
M. Kurouchi, T. Araki, Y. Nanishi
Dept. of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi,
Kusatsu, Shiga 525-8577, Japan
Contactless electroreflectance (CER) spectroscopy is a powerful tool to investigate optical properties of semiconductors. The derivative nature of this experimental method enables observation of a large number of sharp spectral features including this related to the band-gap transition splitted into individual lines associated with particular valence subbands. The issue of the bandgap energy for InN is still not fully understand, especially the structure of the valence band. In this paper two InN samples (S1 and S2) grown by molecular beam epitaxy (MBE) are studied in CER spectroscopy. The electron concentration for sample S1 and S2 is 2.7 and 6.0 1018 cm-3, respectively while the electron mobility for samples S1 and S2 is 1330 and 870 cm2/Vs, respectively. For the two samples CER features related to the band-gap energy are observed around 0.7 eV at room temperature. However, these features cannot be fitted by a one CER resonance. Note that the fine structure of the band-gap transition is visible by nagged eye. It suggest that the valence band at k=0 is splitted into individual subbands. The issue of the valence band structure for InN at k=0 is discussed in this work.