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Carrier distributions in long wavelength quantum dot laser diodes

George, Adrian Alexander 2007. Carrier distributions in long wavelength quantum dot laser diodes. PhD Thesis, Cardiff University.

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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

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
ISBN: 9781303224584
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:13

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