L. Borkovska

Anti-Stokes photoluminescence and structural defects in CdSe/ZnSe nanostructures

Abstract An efficient anti-Stokes photoluminescence (ASPL) in multistacked CdSe/ZnSe nanostructures with quantum dots (QDs) has been found under the excitation below the QD ground states. An efficiency of ASPL is a few percents of the Stokes one. The dependencies of anti-Stokes emission spectra on temperature and excitation density have been studied. It is shown that excitation mechanism of this luminescence at low temperature can be explained by the two-step two-photon absorption process involving deep levels of cation vacancy related defects as intermediate states. It is found that with temperature increase resonant excitation in QD photoluminescence band may occur and contribution of thermal excitation of carriers becomes actual.

Optical investigations of the influence of point defects on quantum dots in CdSe/ZnSe heterostructures

Optical properties of single-layer and multistack CdSe/ZnSe self-assembled quantum dot (QD) heterostructures have been investigated. It is found that QDs at the interface can accumulate cation vacancy-related defects. In this case the level of defects is associated with the quantized heavy-hole level of the QDs. It is shown that study of the excitation spectra of the defect-related band enables one to obtain information about optical transitions in QDs.

Role of Cation Vacancy-Related Defects in Self-Assembling of CdSe Quantum Dots

In this chapter we present the results of the photoluminescent and optical investigations of the influence of cation vacancy-related defects on CdSe/ZnSe quantum dot organization. Selfassembling growth was achieved under molecular beam epitaxy with subsequent annealing step. Number of cation vacancies was controlled by the intensity of the emission band connected with complex that includes cation vacancy and shallow donor. For the first time it is shown that increase of number of cation vacancy related defects results in the reduction of potential fluctuations in the QD layer. In this case a relatively uniform dense array of QDs with shallow localization potential is organized. It is proposed that generation of cation vacancies during the growth suppresses both Cd segregation and Cd surface diffusion as well as facilitates Cd/Zn interdiffusion. Interdiffusion process is proved by the changes in the photoluminescence and optical reflection spectra of ZnSe layers. It is showned that Cd/Zn interdiffusion can play an important role in CdSe/ZnSe intermixing during the QD formation at least under such growth conditions which can stimulate generation of cation vacancies.

Investigation of inhomogeneous broadening of CdSe/ZnSe nanoisland photoluminescence band by resonant excitation methods

Abstract This paper presents the results of photoluminescence and Raman scattering investigations of CdSe/ZnSe nanostructures. Using resonant excitation of Cd-containing nanoislands both Stokes and anti-Stokes emission are observed. The mechanism of anti-Stokes luminescence, including two-photon two-step excitation through the local states of defects and quantized states of islands, is proposed. The inhomogeneous broadening of the photoluminescence band is shown to be largely due to the size distribution of islands and/or to the variation of their Cd-content.