Dependence of energy gap on x and T in Zn1-xMnxSe: The role of exchange interaction

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Photoluminescence and reflectivity measurements have been carried out on Zn1-xMnxSe solid solutions in the complete range of crystal compositions, 0x0.55. The features of the photoluminescence and reflectivity data near the band edge enabled us to determine values of the fundamental band gap as a function of Mn molar fraction x and temperature (8 KT 300 K). The energy gap in crystals with compositions in the vicinity of the zinc-blende wurtzite structural transition (0.2x0.3) exhibited a scatter of values, probably associated with the presence of various polytypes (as evidenced by transmission-electron-microscopy measurements). The dependence of Eg on x is anomalous for 0x0.2, showing a minimum in the Eg vs x curve. A simple model (in terms of second-order perturbation theory in s-d and p-d interactions) relates this minimum to a maximum observed in the magnetic susceptibility as a function of x. For samples with x0.35, the Eg dependence on T shows an onset of an additional blue shift as the temperature is lowered below 150 K. This onset, though not reproduced by our simple calculation, appears to be also related to the presence of s-d and p-d interactions. © 1986 The American Physical Society.

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Physical Review B