Group III-nitride semiconductors are the dominant inorganic solid state light emitting materials, spanning the UV to infra-red spectral range. InGaN/GaN based LEDs and lasers are commercially available and intense research is being pursued to improve their efficiency. One practical approach is the development of functionalised and/or improved materials patterned on a nanometre length scale. This thesis presents the optical, morphological and compositional characterisation of III-nitride based nanostructured light emitters. The III-nitride nanostructures studied are GaN coalesced above arrays of either nanopyramids or nanocolumns, semipolar and nonpolar InGaN QWs on the facets of GaN nanopyramids, and thin epilayers of AlInN and AlInGaN. Spatially resolved optical characterisation of nano-ELOG GaN layers revealed a shift in the exciton-related band edge emission across the coalesced layer. This is related to Si doping and to strain effects. Study of the semipolar {1011} InGaN QWs grown on the facets of GaN nanopyramids identified a blue shift in QW emission energy as the sampled region is moved up the pyramid facets. This shift is found to follow the release of the tensile strain towards the top of nanopyramid. Luminescence properties of nearly lattice matched AlInN epilayers investigated using CL, PL and PLE spectroscopic techniques revealed that the emission and bandgap energy of the AlInN layers are at higher energy than that of GaN. Results obtained from polarisation resolved PL measurements of AlInN epilayers point to two possible implications: the observed higher energy AlInN emission is either related to defects or this emission is due to carrier recombination occurring in InN clusters similar to those of InGaN epilayers. Optical properties of thin AlInGaN epilayers investigated using PL and PLE spectroscopy revealed a redshift in bandgap energy with increase in InN fraction. The observed spatial intensity fluctuations are discussed in terms of the InN compositional fluctuations and inhomogeneous strain effects.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:570586 |
| Date | January 2012 |
| Creators | Krishnan Jagadamma, Lethy |
| Publisher | University of Strathclyde |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=17192 |
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