A photoacoustic spectroscopic investigation of the optical energy gap in Zn-Mn-Se type dilute magnetic semiconductors

Using photoacoustic spectroscopy (PAS) we have measured the composition dep endent optical absorption coefficient and band gap of the Zn1-xMnxSe (0 les s than or equal to x less than or equal to 0.5) diluted magnetic semiconduc tors at room temperature. The band gap E-0 estimated from the PAS spectra v aries nonlinearly, showing a downwards bowing with the Mn-concentration. Th e exchange interaction of electrons in conduction and valence bands with th e d-electrons of Mn ion interactions, effects of polytypes, micro-structure s and mixed crystallization (zinc-blende and wurtzite structures) are consi dered for the analysis of the data. The observed exponential edge (Urbach's edge) can be considered as an internal Franz-Keldish effect arising from t he charged impurity-generated and "frozen-in" optical phonon-generated fiel ds. This can be described in the framework of the Tauc and Dow-Redfield mod el. The phonon-assisted indirect transition at the band tail regions for so me samples are also observed from the present studies. (C) 1999 Published b y Elsevier Science Ltd. All rights reserved.