Electroreflectance studies in Cd1−xMnxTe solid solutions

We present electroreflectance (ER) data near the fundamental absorption edge of Cd1−xMnxTe as a function of temperature and Mn content. We show that the observed weak-field ER structure is associated with the screening of excitons by impact-ionization-generated free carriers. Such a phenomenon has never before been observed in mixed crystals at such high temperatures (300 K). From the increased broadening of the ER structure with composition, we conclude that the excitons have a Wannier-like character for x<0.15 and develop a local bound character for x≳0.15, composition at which the system reaches the percolation critical point. The temperature variation of the energy of transition with composition for x?0.15 is not constant and is believed to be a result of mode softening of the lattice with increased Mn content.