Magnetic field dependence of the exciton bandwidth in diluted magnetic semiconductors with quantum wells

Effects of magnetic impurity concentration and spin-projection fluctuations on the exciton scattering, the exciton bandwidth, and the light reflection, transmission, and absorption spectra of diluted magnetic semiconductor crystals with quantum wells in an external magnetic field were studied. The fluctuations of the distributions of both single and pairs of impurity centres as well as the destruction of antiferromagnetically coupled pairs by a high magnetic field were taken into account. Calculations were performed for the quantum wells (Cd, Mn)Te/CdTe/(Cd, Mn)Te. It was shown, that: (i) the contribution of the exciton scattering to the exciton bandwidth is considerable - it is comparable with the experimentally observed bandwidths for the systems under study; (ii) the bandwidth increases as the magnetic field rises for the sigma (+)-component of the exciton transition, while the bandwidth decreases for the sigma (+)-component. In particular, the exciton scattering probability drops abruptly when the total magnetic moment of the antiferromagnetically bound pair appears, due to the magnetic field-induced destruction of the pairs. The destruction of the pairs leads to narrowing of the sigma (+)-component of the exciton transition. These peculiarities in the magnetic field dependence of the exciton bandwidth were explained by the coherent summation of spin-dependent and spin-independent parts of the interaction between the exciton and the impurities.