Optical properties of Mn-doped InAs and InMnAs epitaxial films

The optical properties of In1-xMnxAs ferromagnetic semiconductors have been measured over the spectral range of 0.05-3.5 eV to determine their electronic structure. For single-phase InMnAs alloy thin films (x<0.01-0.12), a band gap of 0.334 eV, 23 meV lower than InAs, is observed at 295 K. The decrease is attributed to the formation of a shallow manganese impurity band. Reflectance peaks arising from higher lying L-point transitions between the valence band and conduction band are observed in InMnAs thin films. The energy of these transitions decreases with increasing manganese concentration. This demonstrates that the manganese impurity band broadens at the L-point. A broad featureless absorption band was observed between 0.05 and 0.30 eV. This extrinsic absorption band is attributed to light hole to heavy hole inter-valence band transitions. The measured low-frequency optical conductivity is in good agreement with that determined from electrical resistivity measurements. (C) 2003 Elsevier B.V. All rights reserved.