Control of the electronic properties of CdSe submonolayer superlattices via vertical correlation of quantum dots

Abstract

Structural and optical properties of submonolayer CdSe/ZnSe superlattices grown with varying thickness of the ZnSe spacer layer are studied. High-resolution electron microscopy images demonstrate that submonolayer CdSe depositions result in two-dimensional nanoscale CdSe islands which are anticorrelated for spacer layer thicknesses exceeding 3 nm, while predominantly vertically correlated growth occurs for thinner spacers, in agreement with most recent theoretical predictions. Vertical ordering of the CdSe islands leads to two lines in photoluminescence ͑PL͒ and optical reflectance spectra originating from excitons localized at vertically coupled and uncoupled CdSe quantum islands, respectively. In edge PL, these lines exhibit different polarizations: predominantly TM and predominantly TE for coupled and uncoupled states, respectively. Stimulated emission in edge geometry and resonant waveguiding effects are observed for both states. The TE and TM components of the stimulated emission of the same state show an energy splitting. At the highest excitation densities we observe saturation of the stimulated emission in the edge geometry, and the development of a peak in surface emission that is strongly increasing with excitation intensity. This peak is attributed to stimulated emission in surface geometry, which is made possible by the ultrahigh material gain in quantum dots and the self-adjustment of the gain spectrum and the cavity mode. ͓S0163-1829͑99͒02024-X͔

Atomic Ordering in Self-assembled Epitaxial II-VI and IV-VI Compound Semiconductor Quantum Dot Systems

“…This particular result is in good agreement with a HRTEM study by other authors [19] for a very similar (Cd,Zn)Se/ZnSe multilayer structure (with ZnSe cladding layers of a nominal thickness of 3 nm and CdSe sheets of nominally the same thickness as in our study).…”

X-ray diffraction investigation of a three-dimensional Si/SiGe quantum dot crystal

“…[11][12][13][14][15] However, despite the fact that elastic interactions favor lateral ordering of islands as well, they turned out to be rather weak 16 and only rather short-range ordering was observed in the above mentioned systems by atomic force microscopy, transmission electron microscopy, and x-ray diffraction ͑XRD͒. [16][17][18][19][20][21] Apart from vertical island ordering in columnar form, in III-V, 22,23 II-VI, [24][25][26] and IV-VI compounds 27 also oblique ordering was observed, 28 typically for larger spacer layer thicknesses, before for sufficiently wide spacers the ordering finally vanishes. 29 For the PbSe/PbEuTe system the formation of a three-dimensionally ͑3D͒ ordered trigonal island crystal in PbSe island multilayers separated by PbEuTe spacer layers was observed for a certain range of the spacer layer thickness for growth along an elastically soft ͓111͔ direction.…”

Correlation in Vertically Stacked CdSe Based Quantum Islands

“…Early reports cover the dependence of correlation and anticorrelation in short period submonolayer stacks [7] on stacking conditions like barrier thickness. Litvinov et al [8] demonstrated coherently stacked islands obtained at elevated growth temperatures of 400 C in triple stacks if the barrier thickness corresponded to 12-20 monolayers (ML), while for a smaller thickness a complete intermixing due to inter-diffusion occurred.…”