M.Sc Thesis

M.Sc StudentReizer Yulia
SubjectDeterministic Positioning of a Single Quantum dot
in a Pillar Microcavity
DepartmentDepartment of Electrical and Computer Engineering


Quantum dots are localized, nanometer sized, semiconductor structures that create a three-dimensional confinement potential for electrons and holes. An electron-hole pair trapped inside the quantum dot is referred to as 'exciton'. Once the exciton recombines radiatively, a photon is emitted. The wavelength of the emitted photon is proportional to the difference of energy between the electron and hole.

Because of the nanometric size of the quantum dots, the energy levels of the carriers become quantized. Hence, the emitted photons can only have discrete energy levels much like an atom. Based on this similarity, QDs are often referred to as an “artificial atom” and are considered as the solid state analogue of an atom. Because of the ability of the quantum dot to emit a single photon with a distinct energy, quantum dots are often used as a single photon sources in a variety of applications such as quantum information processing and quantum cryptography.

Despite the obvious benefits, the most notable drawback of quantum dots is their random distribution in size, shape, composition and location on the semiconductor substrate. These drawbacks occur as the result of the growth process of the quantum dots and leads to a variation in their optical properties. Also, in order to use quantum dots as a single photon source, a high collection efficiency of the emitted photons is required. For a semiconductor based device, due to total internal reflection, this efficiency is as low as 2% .

In this work we present a method, based on high resolution photoluminescence imaging, for deterministic positioning of a single quantum dot inside an optical device with potentially position uncertainty of 50nm . The fabricated device is tailored to the distinct properties of the individual quantum dot, and is designed to enhance the spontaneous emission rate of the quantum dot using the Purcell effect. This work also presents a novel device fabrication process, based on electron beam lithography, for the fabrication of micro-pillars with various diameters from 2μm to 18 μm with an accuracy of 0.1-0.2μm. This process allows the fabrication of devices up to 6 μm high, with a smooth top, without compromising the surface quality and the symmetry of the sides.