Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584132
Title: Carrier distributions in long wavelength quantum dot laser diodes
Author: George, Adrian Alexander
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2007
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Abstract:
In this thesis I have produced results to show how carriers populate electronic states of InAs quantum dot (QD) laser diodes which operate near 1.3um, especially those which incorporate tunnel injection. I used the segmented contact method to produce modal absorption, modal gain, spontaneous emission and population inversion spectra as a function of photon energy. The spontaneous emission spectra for a high performance QD structure showed an increased population of the higher energy QD states than the tunnel injection structure. Analysis of the carrier distribution within the high performance QD structure revealed that the population of the QD states can be described by Fermi- Dirac statistics (thermally distributed) at 300K. As the temperature is lowered the electron distribution becomes clearly non-thermal, with clear regions of high inversion seen in the lower energy QD states. The higher inversion can be attributed to a reduced population of wetting layer states and as the temperature is lowered it becomes less likely for carriers to excite out of the dot states and thermally redistribute throughout the ensemble. The tunnelling injection structure was shown to exhibit unique features in its carrier distribution as compared to the high performance structure. At 300K the carrier distribution function is populated to thermal levels over energy ranges corresponding to a subset of the QD ground and first excited states. Between these energy ranges there is a region of under populated states shown by a region of low inversion. This suggests dots of a particular size within the ensemble are preferentially populated by the resonant tunnelling process. This results in a reduced spectral broadening of the emission from the QD ensemble. At higher temperature the selective population can still be observed, however it is less pronounced, presumably due to more efficient thermal distribution of electrons at higher temperature
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.584132  DOI: Not available
Keywords: QC Physics
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