Less strain, more gain_nano_patterning III-N thin films

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Conroy, Michele
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University College Cork
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Controlling the growth mechanism for nano-structures is one of the most critical topics in material science. In the past 10 years there has been intensive research worldwide in IIIN based nanowires for its many unique photonic and electrical properties at this scale. There are several advantages to nanostructuring III-N materials, including increased light extraction, increased device efficiency, reduction of efficiency droop, and reduction in crystallographic defect density. High defect densities that normally plague III-N materials and reduce the device efficiency are not an issue for nano-structured devices such as LEDs, due to the effective strain relaxation. Additionally regions of the light spectrum such as green and yellow, once found difficult to achieve in bulk planar LEDs, can be produced by manipulating the confinement and crystal facet growth directions of the active regions. A cheap and easily repeatable self-assembly nano-patterning technique at wafer scale was designed during this thesis for top down production of III-N nanowires. Through annealing under ammonia and N2 gas flow, the first reported dislocation defect bending was observed in III-N nanorods by in-situ transmission electron microscopy heating. By growing on these etched top down nanorods as a template, ultra-dense nanowires with apex tipped semi-polar tops were produced. The uniform spacing of 5nm between each wire is the highest reported space-filling factor at 98%. Finally by using these ultra-dense nanorods bridging the green gap of the light spectrum was possible, producing the first reported red, yellow, green light emission from a single nano-tip.
Conroy, M. 2016. Less strain, more gain_nano_patterning III-N thin films. PhD Thesis, University College Cork.