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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Fabrication and electrical characterisation of quantum dots : uniform size distributions and the observation of unusual electrical characteristics and metastability

James, Daniel January 2010 (has links)
Quantum dots (QDs) are a semiconductor nanostructure in which a small island of one type of semiconductor material is contained within a larger bulk of a different one. These structure are interesting for a wide range of applications, including highly efficient LASERs, high-density novel memory devices, quantum computing and more. In order to understand the nature of QDs, electrical characterisation techniques such as capacitance-voltage (CV) profiling and deep-level transient spectroscopy (DLTS) are used to probe the nature of the carrier capture and emission processes. This is limited, however, by the nature of QD formation which results in a spread of sizes which directly affects the energy structure of the QDs. In this work, I sought to overcome this by using Si substrates patterned with a focused ion beam (FIB) to grow an array of identically-sized Ge dots. Although I was ultimately unsuccessful, I feel this approach has great merit for future applications.In addition, this thesis describes several unusual characteristics observed in InAs QDs in a GaAs bulk (grown by molecular beam epitaxy-MBE). Using conventional and Laplace DLTS, I have been able to isolate a single emission transient. I further show an inverted relation between the emission rate and the temperature under high field (emissions increase at lower temperatures). I attribute this to a rapid capture to and emission from excited states in the QD. In addition, I examine a metastable charging effect that results from the application of a sustained reverse bias and decreases the apparent emission rate from the dots. I believe this to be the result of a GaAs defect with a metastable state which acts as a screen, inhibiting emission from the dots due to an accumulation of charge in the metastable state. These unusual characteristics of QDs require further intensive work to fully understand. In this work I have sought to describe the phenomena fully and to provide hypotheses as to their origin.

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