Theory of the electronic and optical properties of dilute bismide alloys

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dc.contributor.advisor O'Reilly, Eoin P. en Broderick, Christopher A. 2015-11-24T12:48:23Z 2015 2015
dc.identifier.citation Broderick, C. A. 2015. Theory of the electronic and optical properties of dilute bismide alloys. PhD Thesis, University College Cork. en
dc.description.abstract Dilute bismide alloys, containing small fractions of bismuth (Bi), have recently attracted interest due to their potential for applications in a range of semiconductor devices. Experiments have revealed that dilute bismide alloys such as GaBixAs1−x, in which a small fraction x of the atoms in the III-V semiconductor GaAs are replaced by Bi, exhibit a number of unusual and unique properties. For example, the band gap energy (E g) decreases rapidly with increasing Bi composition x, by up to 90 meV per % Bi replacing As in the alloy. This band gap reduction is accompanied by a strong increase in the spin-orbit-splitting energy (ΔSO) with increasing x, and both E g and ΔSO are characterised by strong, composition-dependent bowing. The existence of a ΔSO > E g regime in the GaBixAs1−x alloy has been demonstrated for x ≳10%, a band structure condition which is promising for the development of highly efficient, temperature stable semiconductor lasers that could lead to large energy savings in future optical communication networks. In addition to their potential for specific applications, dilute bismide alloys have also attracted interest from a fundamental perspective due to their unique properties. In this thesis we develop the theory of the electronic and optical properties of dilute bismide alloys. By adopting a multi-scale approach encompassing atomistic calculations of the electronic structure using the semi-empirical tight-binding method, as well as continuum calculations based on the k•p method, we develop a fundamental understanding of this unusual class of semiconductor alloys and identify general material properties which are promising for applications in semiconductor optoelectronic and photovoltaic devices. By performing detailed supercell calculations on both ordered and disordered alloys we explicitly demonstrate that Bi atoms act as isovalent impurities when incorporated in dilute quantities in III-V (In)GaAs(P) materials, strongly perturbing the electronic structure of the valence band. We identify and quantify the causes and consequences of the unusual electronic properties of GaBixAs1−x and related alloys, and our analysis is reinforced throughout by a series of detailed comparisons to the results of experimental measurements. Our k•p models of the band structure of GaBixAs1−x and related alloys, which we derive directly from detailed atomistic calculations, are ideally suited to the study of dilute bismide-based devices. We focus in the latter part of the thesis on calculations of the electronic and optical properties of dilute bismide quantum well lasers. In addition to developing an understanding of the effects of Bi incorporation on the operational characteristics of semiconductor lasers, we also present calculations which have been used explicitly in designing and optimising the first generation of GaBixAs1−x-based devices. en
dc.description.sponsorship Irish Research Council (EMBARK Initiative RS/2010/2766) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2015, Christopher A. Broderick. en
dc.rights.uri en
dc.subject Semiconductors en
dc.subject Photonics en
dc.subject Condensed matter theory en
dc.title Theory of the electronic and optical properties of dilute bismide alloys en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text not available en Indefinite en 10000-01-01
dc.description.version Accepted Version
dc.contributor.funder Irish Research Council en
dc.description.status Not peer reviewed en Physics en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Yes en
dc.thesis.opt-out true
dc.check.embargoformat Not applicable en
dc.internal.conferring Summer Conferring 2015

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© 2015, Christopher A. Broderick. Except where otherwise noted, this item's license is described as © 2015, Christopher A. Broderick.
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