טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentFradkin Leonid
SubjectMagneto-Optical Properties of Composite Semiconductor
Quantum Dots
DepartmentDepartment of Chemistry
Supervisor Professor Efrat Lifshitz


Abstract

The research focused on the chemical identification of localization sites (core, shell or interface) of photo-generated carriers in spherical semiconductor nanocrystals (NCs) coated by organic or inorganic epitaxial layers (core-shell structures), and elucidates the influence of the surface/interface quality on the optical properties of the materials. The nanocrystals were investigated by the following techniques: photoluminescence, circular and linear polarization photoluminescence, and optically detected magnetic resonance spectroscopy (ODMR), in both the continuous wave mode and the time resolved mode. The ODMR method provides means to identify the surface/interface sites and to correlate them with specific optical transition. In addition, this method reveals information about the angular momentum of band edge and trapped states and about the exchange interaction between trapped electrons and holes, determines the spectroscopic g-factors , distinguishes between the radiative and non-radiative characteristic of a trapping site, and evaluates the spin-lattice relaxation times.

            Following materials have been studied: HgTe/HgxCd1-xTe(S) core-shell structures; InP/ZnS core-shell and InP NCs capped with various organic ligands, and InP nanorods. For the HgTe/HgxCd1-xTe(S) NCs it was demonstrated that the luminescence at the shell regime is associated with a trap-to-band recombination emission, with a relatively long lifetime. The complementary use of an ODMR and circular polarized photoluminescence technique leads for determination of the g factors for the excitons, electron and hole in the InP nanocrystals. The dependence of electron g factors on the size, shape and surface of the InP nanocrystals was shown and compared with theory.