טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBenny Yael
SubjectExperimental and Theoretical Investigations of Many
Carriers' States in Semiconductor Quantum Dots
DepartmentDepartment of Physics
Supervisor Professor David Gershoni
Full Thesis textFull thesis text - English Version


Abstract

We present experimental and theoretical study of single semiconductor quantum dots excited by resonantly tuned variably polarized lasers. We examine neutral, positive charged and negative charged single QDs. For neutral QD we use two non-degenerate tuned variably polarized lasers. The first laser is tuned to excitonic resonances. Depending on its polarization it photogenerates a coherent single exciton state. The second laser is tuned to biexciton resonances. By scanning the energy of the second laser for various polarizations of the two lasers, while monitoring the emission from the biexciton and exciton spectral lines, we map the biexciton photoluminescence excitation spectra. For charged QD we use one polarized laser, tuned to trionic resonances, while monitoring the emission from the ground state trion and

first excited spin-blockaded trions. The resonances rich spectra of the absorption are analyzed and fully understood in terms of a many carrier theoretical model which takes into account the direct and exchange Coulomb interactions between the quantum confined carriers.

Identifying the neutral lines, we demonstrate a one to one correspondence between the polarization state of a light pulse tuned to neutral exciton resonances of single semiconductor quantum dots and the spin state of the exciton that it photogenerates. This is accomplished using two variably polarized and independently tuned picosecond laser pulses. The first “writes” the spin state of the resonantly excited exciton. The second is tuned to biexcitonic resonances, and its absorption is used to “read” the exciton spin state. The absorption of the second pulse depends on its polarization relative to the exciton spin direction. Changes in the exciton spin result in corresponding changes in the intensity of the photoluminescence from the biexciton lines which we monitor, obtaining thus a one to one mapping between any point on the Poincare sphere of the light polarization to a point on the Bloch sphere of the exciton spin.