EXCITONIC STATES AND THE INFLUENCE OF THE EXCHANGE INTERACTION IN THE SEMIMAGNETIC SEMICONDUCTOR CADMIUM(1-X) MANGANESE(X) SELENIUM.

摘要

The results of a photoluminescence spectroscopy study of the properties of excitonic states under the influence of the exchange interaction with the Mn('++)-ion spins in the semimagnetic semiconductor Cd(,l-x)Mn(,x)Se are presented. It is found that, in the absence of an external magnetic field, the donor-bound exciton energy shows unusual dependences on temperature and Mn composition. This is interpreted to be a consequence of a local magnetization of the Mn('++)-ion spins within the bound exciton volume. The finite size magnetization effect on the bound exciton energy is qualitatively explained if both the thermodynamic fluctuations of the Mn('++)-ion spin cloud and the influence of the localized carriers on the spin state of the Mn('++)-ions are considered. The latter results in the formation of a bound magnetic polaron for x = .10 Mn concentration (the highest studied) at T < 10 K. With increasing temperature, a transition from a magnetic polaron regime to a fluctuation dominated regime is observed for this composition.; The possibility of a long-range, magnetically ordered state in Cd(,l-x)Mn(,x)Se at low temperatures (T = 1.8 K), induced by the exchange interaction between the Mn('++)-ion spins and a dense electron-hole plasma generated by intense optical excitation has also been investigated. The observed luminescence spectra yield information about the temporal evolution of inelastic scattering processes in a dense exciton gas, with a likely contribution by an electron-hole plasma. The short carrier lifetimes measured, less than 100 psec for x = .10, together with possible plasma expansion may prevent the realization of a spin ordered state under our experimental conditions.