Forster theory of energy transfer is applied in diluted systems, and yet it remains unknown if it can be applied to the dense media. We have studied the exciton transfer in one-dimensional (1-D) close-packed pure and mixed quantum dot (QD) array under different models and two-dimensional (2-D) perfect lattice. Our approach is based on the master equation created by treating the exciton relaxation as a stochastic process. The random parameter has been used to describe dot-to-dot distance variations. The master equation has been investigated analytically for 1-D and 2-D perfect lattices and numerically for 1-D disordered systems. The suitability of Forster decay law on the excitation decay of close-packed solid has been discussed. The necessity to consider the effect of the further nearest interdot interactions has been checked. / Department of Physics and Astronomy

In the field of spintronics there is a strong need for an efficient spin-polarizing device. To that end, two basic devices are proposed: a series of Aharonov-Bohm (AB) rings linked in series with intermediate quantum dots (IQD) and the quantum dot spin polarizer (QDSP). In each case the system is built of quantum dots (QD), each of which can be Zeeman split with a tunable external magnetic field. Spin neutral input and output leads are also attached to each system. The Tight Binding Approximation (TBA) is used to model each system. Mathematica is used to solve the systems generated by TBA, so that the transmission or reflection of a system can be evaluated. We find that a series of AB rings provides for wide, energetically separated, spin polarized conduction bands. The QDSP provides physical separation of spin polarized electrons, making a spin polarized base current possible. / Methods of analysis -- The Aharonov-Bohm ring -- The quantum dot spin-polarizer. / Department of Physics and Astronomy

We numerically investigate a total transmission probability through QDs embedded in an AB ring. The QDs are formed by delta function-like double potential barriers and a magnetic flux is penetrated in the center of the ring. In particular, we study the coupled double-QDs in series and non-coupled double-QDs in parallel in an AB ring. In each model, we show the total transmission probability as a function of QD size and electron incident energy, and present the transmission amplitude on the complex-energy plane. Of interest is the change and progression of Fano resonances and corresponding zero-pole pairs on the complex-energy plane with magnetic flux in the center of the ring.To accomplish this, we analytically solve the scattering matrix at each junction and the transfer matrix through the arms of the ring using Schrodinger equation for the delta function barriers. Then, the total transmission probability is obtained as a function of electron energy and magnetic flux by cascading these matrices. Finally, the solutions of the analytical equations and the graphical output of the transmission characteristics in the system will be obtained numerically by using Mathematica programs run on desktop computers. / Department of Physics and Astronomy