MAGNETIC-FIELD-DEPENDENT AND TEMPERATURE-DEPENDENT EXCITON DELOCALIZATION IN A CDTE/CD1-XMNXTE SUPERLATTICE

Reflectivity and photoluminescence studies have been made on a CdTe/Cd1-xMnxTe superlattice containing a single extended well, wider by one molecular monolayer. Excitonic transitions are observed between both the superlattice Bloch states and the confined extended well states. At low temperatures, relatively long radiative lifetimes allow the carriers to move freely through the superlattice until they become localised in the extended well. As the temperature is increased, the excitons become thermally delocalised into the superlattice. In an applied magnetic field, exchange interactions in the dilute magnetic barriers reduce the confinement potentials for the m(j) = -t/2, -3/2 components. As the field is increased. the sigma+ exciton states again become delocalised into the superlattice. The reduction in barrier height leads to a type-II band alignment for the m(j) = -3/2 spin component, for which the extended well becomes a barrier, further delocalising the sigma+ exciton states. The effect of the transition to a type-II structure allows us to deduce a valence band offset of 17%.