טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYaron Kodriano
SubjectOptical Studies of Quantum Dots in Photonic Structures
DepartmentDepartment of Physics
Supervisor Full Professor Gershoni David
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

We studied the optical properties of single layer of self assembled semiconductor quantum dots embedded in the anti-node of a microcavity. Two kinds of sample are studied. The first one is a planar microcavity that confines the electromagnetic radiation only in one dimension. In the second one small micropillars are fabricated such that the electromagnetic field is confined in all three dimensions to a small volume.

In the planar sample we observed spontaneous localization of the electromagnetic radiation in the plane of the sample. These localized modes have lower energies than the energy of the planar microcavity mode.

By measuring the spatial distribution of the intensity of these modes, we show that the modes are confined into a volume which is comparable to the wavelength of the radiation in the matter, cubed.

We explain this novel observation in terms of a statistical model for estimating the shape of the most probable fluctuation in the spatial distribution of the dielectric constant. These fluctuations are formed by random fluctuations in the areal density of the self assembled quantum dots. The model provides estimation for the probability per unit area to find a confined mode of a given energy in the planar sample.

We used high resolution, polarization sensitive spectroscopy at various temperatures of the micropillars samples. This way we were able to bring the quantum dot emission into resonance with the micropillar cavity mode. We studied micropillars in the strong and in the weak coupling regimes. In the strong coupling regime we measured anti-crossing of 46 μeV when the two modes brought together. This represents coupling constant of about 34 μeV between the quantum dot dipole moment and the micropillar cavity. In the weak coupling regime a Purcell enhancement factor of about 3 was demonstrated.

 From the polarization sensitive measurements we found that the cavity mode itself is split into two orthogonal linearly polarized modes, probably due to residual asymmetry in the fabricated pillar. The quantum dot emission changes its polarization while it is tuned in and out of resonance with the cavity mode. In both cases it assumes the polarization of the energetically closed linearly polarized component of the split cavity mode.