Luminescence of excitons localized by monolayer interface fluctuations in ZnSe/MgS superlattices grown by metalorganic vapor phase epitaxy

Luminescence properties of ZnSe/MgS superlattices (SLs) grown by metalorganic vapor phase epitaxy (MOVPE) were characterized using photoluminescence (PL) and reflection measurements. At low temperature, PL peaks originating from localized excitons which were confined by monolayer fluctuations were clearly observed. It was found that the luminescence efficiency of localized excitons was very high, probably nearly 100%. The thermalization of localized excitons to free excitons with the increase of temperature leads to a blue shift of the PL peak energy and an abrupt decrease of the luminescence intensity. This decrease of the luminescence intensity is attributed to the capture of free excitons by nonradiative centers. A SL which shows luminescence from continuously distributed tailed states exhibited a temperature dependence much different from that of the above SLs which show luminescence from the localized excitons defined by the interface fluctuations.