Optimisation of high-efficiency UV and visible light sources utilising lateral localisation in InAlN and InGaN based nano-structure devices

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dc.check.embargoformatEmbargo not applicable (If you have not submitted an e-thesis or do not want to request an embargo)en
dc.check.infoNot applicableen
dc.check.opt-outNot applicableen
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dc.contributor.advisorParbrook, Peter Jamesen
dc.contributor.authorNorouzian Alam, Shahab
dc.contributor.funderIranian Ministry of Science, Research & Technologyen
dc.contributor.funderScience Foundation Irelanden
dc.date.accessioned2019-03-19T11:48:52Z
dc.date.available2019-03-19T11:48:52Z
dc.date.issued2018
dc.date.submitted2018
dc.description.abstractIII-nitride semiconductor materials (including GaN, InN and AlN and their alloys), have the capability to emit light at wavelengths spanning from the near IR to the deep UV. However, understanding these materials is challenging due to the presence of strong polarisation fields and large difference in optimum growth temperature between binary compounds are two such examples. InAlN is perhaps the least well understood III-N alloy. It has potential be applied for optoelectronic devices operating in the UV spectral range. However, the variation of band-gap with alloy composition, particularly in the low In content regime, is not understood. In this work, a strongly composition dependent bowing parameter has been observed for ~100 nm thick InxAl1−xN epitaxial layers with 0 ≤ x ≤ 0.224, grown by metalorganic vapour phase epitaxy (MOVPE), prepared on AlN/Al2O3-templates. Also a double absorption edge was observed for InAlN with x < 0.01, attributed to crystal-field splitting of the highest valence band states. These results indicate that the ordering of the valence bands is changed at much lower In contents than linear interpolation of the valence band parameters would predict. Coupling our results with the published literature data the band-gap and bowing parameter of InAlN across the full composition range were determined. Additionally, applying the InAlN band-gap data with those for other alloys the refractive index of III-N alloys is predicted using an Adachi model resulting in a very good agreement with previous experimental data where available. For InAlN/AlGaN multi-quantum-wells (MQWs) excited by photoluminescence (PL) and emitting between 300-350 nm, high apparent internal quantum efficiencies (IQE) (IPL(300 K)/IPL(T)max) of up to 70% were obtained. This is attributed to the exceptionally strong carrier localisation in this material, which is also manifested by a high Stokes shift (0.52 eV) of the luminescence. A non-monotonic dependence of luminescence efficiency on indium content with a maximum at about 18% In was explained as a trade-off between a strain relaxation for higher indium contents and a type I to type II band line-up conversion for low In content alloys. Nanoscale materials have attracted a lot of attention due to their ability to decrease dislocations as well as build-in field reduction. In the second part of this thesis, GaN nanostructures, were used as templates for InGaN MQW growth targeting nano-LED structures. Two nano-structuring methods were examined; using GaN nano-columns (NCs) following an etch regrowth methodology, and selective area aperture growth (SAG). In the former case we determined the optimal etch conditions for the GaN columns and conditions for overgrowth InGaN QWS. The rod tops formed semipolar facets. InGaN QWs grown on these pyramids were found to be extremely thin leading to difficulties in obtaining PL in our case. Using the SAG approach, nano-pyramids were formed in nano-apertures, with good uniformity. InGaN QWs exhibited blue PL, which cathodoluminescence (CL) showed to be made up of two spectral features, attributed to the pyramid nano-facets and pyramid apex tips, respectively.en
dc.description.statusNot peer revieweden
dc.description.versionAccepted Version
dc.format.mimetypeapplication/pdfen
dc.identifier.citationNorouzian Alam, S. 2018. Optimisation of high-efficiency UV and visible light sources utilising lateral localisation in InAlN and InGaN based nano-structure devices. PhD Thesis, University College Cork.en
dc.identifier.endpage211en
dc.identifier.urihttps://hdl.handle.net/10468/7639
dc.language.isoenen
dc.publisherUniversity College Corken
dc.rights© 2018, Shahab Norouzian Alam.en
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/3.0/en
dc.subjectIII-nitrideen
dc.subjectGaNen
dc.subjectInNen
dc.subjectAlNen
dc.subjectBand-gapen
dc.subjectPhotoluminescenceen
dc.subjectPhotonicsen
dc.subjectSemiconductor materialsen
dc.subjectGallium nitrideen
dc.subjectNano structureen
dc.thesis.opt-outfalse
dc.titleOptimisation of high-efficiency UV and visible light sources utilising lateral localisation in InAlN and InGaN based nano-structure devicesen
dc.typeDoctoral thesisen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhDen
ucc.workflow.supervisorpeter.parbrook@tyndall.ie
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