Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.822953
Title: Characterising the optical properties of nano-structured semiconductor materials
Author: Southern-Holland, Rachel
ISNI:       0000 0005 0289 3751
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Abstract:
In this work, the optical properties of semiconductor materials were studied. Firstly, bismuth-containing silica thin film samples were measured that had been co-implanted with either Al or Si. Samples that underwent a rapid thermal annealing, did not exhibit the broadband NIR emission as expected. Rutherford backscattering spectroscopy found that Bi was being lost from the samples post-anneal, with the hottest anneals losing the most Bi and that higher concentrations of Al helped to retain more Bi. Lower temperature anneals exhibited a weak bismuth signal in samples with high Bi and Al implants, with the most pronounced signal at 700C 45 minute anneals. Temperature dependent pho- toluminescence (PL) of a bismuth-doped silicon oxynitride film showed that the emission was independent of the temperature. Secondly, various silicon nanocrystal (Si-nc) samples were studied. The optical gain of two samples with different sized Si-ncs was measured. It was found that the sample with the larger Si-ncs, exhibited a smaller gain and that this was due to this sample having a larger absorption. The gain of Si-nc samples with different concentrations of co-implanted erbium were also measured. For the Si-nc signal, a positive gain was measured for wave- lengths between 650-900nm. However, the sample with no Er exhibited a maximum gain of 13cm-1, with the maximum gain increasing to 32cm-1 for the 0.3x1016cm-2 Er sample, with a subsequent decrease in gain for an increase in the Er concentration. This is possibly due to the Si-ncs transferring energy to the Er centres. Gain measurements of the erbium signal of the sample containing 0.3x1016cm-2 of Er, found a large gain of 230cm-1, which again may be due to energy being transferred to the Er from Si-ncs. Time dependent gain taken of the sample with no Er found very little gain, that was independent of the time from the pump pulse. Lastly, InGaN/GaN multiple quantum well samples were measured. Power dependent gain measurements of sample GN1720 showed a reduction in the width of the positive gain band and a redshifting of the maximum gain with a reduction in pump intensity. For sample GN1717 only small differences in the gain were measured for wavelengths between 500-700nm. However, for both samples, the maximum gain was not seen at the maximum power and this may be due to higher free carrier absorption at this intensity. Power dependent PL, showed a large blueshift in emission for polar samples and a much reduced blueshift for semi-polar samples due to a reduced quantum confined stark effect (QCSE). The samples with a higher In content for each of the polar and semi-polar samples had the most blueshift due to more strain-induced QCSE. "Chevron" defect features, on sample GN2733, were studied via PL mapping and showed a 10nm redshift in emission and a reduction in intensity at the \join" of the chevron, possibly due to a higher In content here. A Raman map of the chevron showed an increase in frequency at the join for the A1 & E1 longitudinal optic (LO) mode. Polarised Raman mapping was conducted to try to measure the InGaN layer, the maps again exhibited a similar shift for the A1 & E1 mode at angles and polarisations where the intensity of this mode was high and low, indicating the scattering did not originate in the InGaN layer. As this shift was not seen at other modes it was attributed to LO phonon-plasmon coupling. IR resonant Raman measurements at the chevron join and away from it, showed no significant differences in their spectra.
Supervisor: Halsall, Matthew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.822953  DOI: Not available
Keywords: Variable Stripe Length ; Photoluminescence ; Raman Spectroscopy ; Silicon Nanocrystals ; Bismuth ; InGaN/GaN MQW
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