13. Tutkimustietoportaalin artikkelit / Articles in the Research information portal

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https://aaltodoc.aalto.fi/handle/123456789/21256
Yliopiston tutkimustietojärjestelmään tallennetut avoimet julkaisut sekä EU-rahoitteisten projektien tutkimustuotokset.
Open access publications deposited in the university’s research information system, as well as research outputs from EU-funded projects.

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Browsing 13. Tutkimustietoportaalin artikkelit / Articles in the Research information portal by Author ""O'Reilly", Eoin P."

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    Atomistic analysis of the impact of alloy and well-width fluctuations on the electronic and optical properties of InGaN/GaN quantum wells
    (2015) Schulz, Stefan; Caro, Miguel A.; Coughlan, Conor; "O'Reilly", Eoin P.; Department of Applied Physics; Department of Electrical Engineering and Automation; Computational Soft and Molecular Matter
    We present an atomistic description of the electronic and optical properties of In0.25Ga0.75N/GaN quantum wells. Our analysis accounts for fluctuations of well width, local alloy composition, strain and built-in field fluctuations as well as Coulomb effects. We find a strong hole and much weaker electron wave function localization in InGaN random alloy quantum wells. The presented calculations show that while the electron states are mainly localized by well-width fluctuations, the holes states are already localized by random alloy fluctuations. These localization effects affect significantly the quantum well optical properties, leading to strong inhomogeneous broadening of the lowest interband transition energy. Our results are compared with experimental literature data.
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    Atomistic description of wave function localization effects in In(x)Ga(1-x)N alloys and quantum wells
    (2015) Schulz, Stefan; Marquardt, Oliver; Coughlan, Conor; Caro, Miguel A.; Brandt, Oliver; "O'Reilly", Eoin P.; Department of Applied Physics; Department of Electrical Engineering and Automation
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    Origin of nonlinear piezoelectricity in III-V semiconductors: Internal strain and bond ionicity from hybrid-functional density functional theory
    (2015) Caro, Miguel A.; Schulz, Stefan; "O'Reilly", Eoin P.; Department of Applied Physics; Department of Electrical Engineering and Automation
    We derive first- and second-order piezoelectric coefficients for the zinc-blende III-V semiconductors {Al,Ga,In}−{N,P,As,Sb}. The results are obtained within the Heyd-Scuseria-Ernzerhof hybrid-functional approach in the framework of density functional theory and the Berry-phase theory of electric polarization. To achieve a meaningful interpretation of the results, we build an intuitive phenomenological model based on the description of internal strain and the dynamics of the electronic charge centers. We discuss in detail first- and second-order internal strain effects, together with strain-induced changes in ionicity. This analysis reveals that the relatively large importance in the III-Vs of nonlinear piezoelectric effects compared to the linear ones arises because of a delicate balance between the ionic polarization contribution due to internal strain relaxation effects, and the contribution due to the electronic charge redistribution induced by macroscopic and internal strain.