|Ph.D Student||Langof Lidia|
|Subject||Magneto-Optical Studies of III-V Semiconductor Nanocrystals|
|Department||Department of Physics||Supervisors||Professor Emeritus Eitan Ehrenfreund|
|Professor Efrat Lifshitz|
This thesis reports the magneto-optical studies of low-dimensional semiconductor quantum structures¾nanocrystals. These structures have become a subject of great interest due to their unique electronic and optical properties. However, these properties are strongly influenced by the nature of the surfaces and interfaces.
The work presented is concerned with the investigation of the optical properties of the nanocrystals and the surface sites of the nanocrystals and quantum wells. The nanocrystals were investigated by the following techniques: photoluminescence, photoluminescence polarization, and optically detected magnetic resonance spectroscopy (ODMR), in both the continuous wave mode and the time resolved mode.
Research has shown that intense band edge emission of colloidal InP nanocrystals is achieved after etching of the nanocrystals with HF or by coating them with a layer or shell of a different semiconductor (ZnS). Three samples were examined and compared: InP non-etched, InP etched, and InP/ZnS core shell nanocrystals.
In the ODMR experiment, a change in luminescence intensity, resulting from a magnetic resonance event at the excited state is monitored. The ODMR spectra of the InP samples were measured as a function of the laser power, microwave power, microwave modulation frequencies, and light polarization. The results show that the defect luminescence originates from a weakly coupled electron-hole pair, where the electron is trapped at the surface by phosphorous vacancy, and the hole is located at the valence band. Additionally, the results suggest that the non-etched samples are dominated by phosphorus vacancy (Vp) at the surface. The surface Vp are largely eliminated upon HF treatment, leaving behind a small percent of Vp in the core of the nanocrystal. The electron-hole exchange interaction was also established from circular polarized ODMR measurements. The time resolved ODMR measurement further clarified the spin dynamics and characteristics of the magnetic sites.