The photoluminescence from ZnS/(ZnSe)1/ZnS heterostructures

Using the concept developed previously on the temperature dependence of the radiative lifetime of confined excitons in low dimensional systems, we have investigated the ZnS/(ZnSe)1/ZnS single quantum well systems by picosecond optical measurement techniques. It is found that the radiative lifetime of the confined exciton in the 1 monolayer (ML) ZnSe system is independent of temperature below 40 K, a result which is fundamentally different from the behavior of the 5 ML ZnSe system. The 1 ML system thus shows the property of a quantum dot system. In addition, it is observed that quantum wells thicker than 3 ML emit a sharp excitonic luminescence while those thinner than 2 ML emit a broad luminescence. We propose that such behaviour is caused by the lateral quantum confinement effect in ‘quantum slabs’ formed on islands and valleys at the interface. The characteristic decay curve of the 1 ML system is close to that of a stretched exponential. This means that this is a random system since it is composed of quantum slab boxes of random size and shape since the characteristic dimensions and shape of the islands and valleys at the interface are themselves random. The effective lateral size along the interface is estimated as ~ 600 nm2 for the 1 ML system.