Ultra-thin quantum wells and fractional monolayer quantum dots of II-VI semiconductors for optoelectronic applications

We will present the results of the combined growth by molecular beam epitaxy (MBE) and atomic layer epitaxy (ALE) of CdSe/ZnSe and CdTe/ZnTe ultra-thin quantum wells (UTQWs), characterized by means of photoluminescence spectroscopy (PL). In spite of its reduced thickness, a single QW, few monolayers (ML) thick, is able to produce bright emission even under low power excitation. These nanostructures are of great interest for optoelectronic applications such as LEDs and diode lasers. In-situ, reflection high energy electron diffraction (RHEED) experiments indicated the 2D growth of the UTQWs and the real-time temporal analysis of the intensity of RHEED pattern features demonstrated the absence of degradation of their structural quality during the ALE growth. Fractional monolayer quantum dots (FMQDs) produced by the deposition of ∼0.5 ML of CdSe present very intense and narrow deep blue excitonic emission. The sharp luminescence of the FMQDs is indicative of their highly uniform size and shape. Even though the 1ML QWs are very thin, the calculated transitions obtained by means of the envelope function in the effective mass approximation are in quite good agreement with the observed excitonic transitions.