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Rita Najjar

Epitaxy of II-VI semiconductors: ZnTe/ZnSe and CdTe:Se. Study of the electronic confinement in type-II heterostructures and isoelectronic doping

Published on 12 December 2008


Thesis presented December 12, 2008

Abstract:
This work is based on the growth, by molecular beam epitaxy, of semiconductor heterostructures in which tellurium and selenium coexist. The goals are to develop optimized growth conditions and to study the specific physical properties due to this coexistence. More specifically, we worked on ZnTe/ZnSe type-II quantum wells and quantum dots, and on isoelectronic centers CdTe: Se.
For ZnTe highly strained on ZnSe we observed a Stranski-Krastanov like relaxation and surface reorganization, but with large scale undulations. Nevertheless we managed to obtained nanometer scale islands thanks to a surface treatment based on amorphous tellurium deposition and sublimation. Then we were faced with difficulties regarding islands capping to form quantum dots. Under usual ZnSe growth conditions, the ZnTe islands are fully flattened and disappear. We propose new growth conditions to preserve the islands and obtain 0D confinement. We observe that the nanostructures we developed are never based on pure ZnTe in ZnSe but on ordered alloy ZnSeTe which forms spontaneously.
We studied in details the photoluminescence and time resolved photoluminescence properties of thin ZnTe/ZnSe quantum wells and of ZnTe/ZnSe quantum dot planes. The huge difference observed between those two kinds of samples is fully explained by a model based on electrostatic and statistical peculiarity of confinement in the case of type-II band alignment.
The last part of this manuscript is dedicated to the delta-doping of CdTe with selenium. We succeeded in isolating a single selenium based localization center and study the anti-bunching of photons emitted by such centers, proving that they behave as single photons emitters.

Keywords:
Quantum Dots, Molecular Beam Epitaxy, II-VI Semiconductor : tellurium and selenium, electronic confinement in type-II heterostructures, isoelectronic doping

On-line thesis.