SURFACE LUMINESCENCE OF A2B6 SEMICONDUCTOR QUANTUM DOTS (REVIEW)

Abstract

Semiconductor zero-dimensional nanocrystals – quantum dots (QDs) – have been increasingly used in various fields of opto- and nanoelectronics in recent decades. This is because of the exciton nature of their luminescence, which can be controlled via the well known quantum-dimensional effect. At the same time, at small nanocrystall sizes, the influence of the surface on the optical and structural properties of nanocrystals increases significantly. The presence of broken bonds of surface atoms and point defects – vacancies and interstial atoms – can both weaken the exciton luminescence and create new effective channels of radiant luminescence. In some cases, these surface luminescence becomes dominant, leading to optical spectra broadening up to the quasi-white light. The nature of such localized states often remains unestablished due to the large number of the possible sorts of defects in both of QD and its surrounding. In contrast to exciton luminescence, which can be properly described within effective-mass approximations, the optical properties of defects relay on chemical nature of both defect itsself and its surrounding, what cannot be provided by “hydrogen-type coulomb defect” approximation. Moreover, charge state and related to this lattice relaxation must be taken into account, what requires an application of atomistic approach, such as Density functioal theory (DFT). Therefore, this review is devoted to the study of surface (defect) states and related luminescence, as well as the analysis of possible defects in nanocrystals of semiconductor compounds A2B6 (CdS, CdZnS, ZnS), responsible for luminescence processes, within ab initio approach. The review presents the results of the authors' and literature sources devoted to the study of the luminescent characteristics of ultra-small (<2 nm) QDs.