Electronic phenomena in self -organized quantum dots: Theory and applications.

Abstract

Self-organized quantum dots provide great promise for many novel electronic and optoelectronic devices. This work focuses on various aspects electron transport in heterostructures, which include self-organized quantum dot layers. Tunneling between pairs of laterally and vertically coupled InAs and In_0.4Ga_0.6As quantum dots is investigated from a theoretical perspective. Vertical tunneling can be quite fast, but lateral tunneling, on the other hand, is quite slow due to the rather large tunneling distances involved. The vertical tunneling rate is found to agree quite well with the results measured by differential transmission experiments. Lateral transport through quantum dot layers is also studied, both experimentally and theoretically and both at low fields and at high fields. The dominant mechanism of such lateral transport is via hopping conduction at low temperatures and via thermal activation at high temperatures. In addition to studying the material properties of self-organized quantum dot heterostructures, devices, which take advantage of the properties, were also investigated. The excited carrier lifetime in quantum dot inter-subband detectors is calculated using a Monte Carlo model, which reveals that the lifetime increases as the applied bias is increased. By increasing the bias under which the device is place, the electrons become more energetic and therefore less likely to be captured. Detector parameters such as photoconductive gain are calculated which agree with previous experimental results. Finally, a vertical quantum dot FET is designed and fabricated. The source-drain current of this device shows a large negative differential resistance at room temperature.