Fabrication of ZnS/(ZnSe)_n/ZnS single quantum well structures and photoluminescence properties

ZnS/ZnSe single quantum well structures are fabricated for the first time by a combination of molecular beam epitaxy and atomic layer epitaxy. The quantum wells thicker than 3 monolayers (ML) emit a sharp excitonic emission with half width of 15-30 meV, while a broad emission (half width of around 100 meV) with low-energy tail is observed from quantum wells thinner than 2 ML. From the analysis of the dependence of emission energy on well width, it is concluded that the conduction band offset at the ZnSe/ZnS interface is very small (almost zero). It is suggested that the luminescence broadening in thin quantum wells is caused by fluctuations not only associated with the quantum confinement effect along the growth direction, but also with the lateral quantum confinement effect in "quantum slabs" formed on islands and valleys at the interface.