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Band gap reduction and dielectric function of Ga1-xZnxN1-xOx and In1-xZnxN1-xOx alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0002-9050-5445
2012 (English)In: Physica Status Solidi. A: Applications and Materials Science (Print), ISSN 1862-6300, Vol. 209, no 1, 75-78 p.Article in journal (Refereed) Published
Abstract [en]

The band gap reductions, dielectric functions and absorption coefficients of the Ga1-xZnxN1-xOx and In1-xZnxN1-xOx (x=0.00, 0.25, 0.50, 0.75, and 1.00) alloys were calculated, employing the partial self-consistent GW approximation. As a comparison, the local density approximation (LDA) and the Heyd-Scueria-Ernzerhof (HSE) hybrid functional were also used to calculate the gap reduction. Both Ga1-xZnxN1-xOx and In1-xZnxN1-xOx alloys show strong band gap bowing. As a result, the band gap energy in Ga1-xZnxN1-xOx is reduced by E-g(GaN) E-g (Ga1-xZnxN1-xOx) - 1.61, 2.01 and 1.91 eV for x=0.25, 0.50, and 0.75, respectively. This allows optoelectronic devices based on GaN and ZnO with more efficient absorption or emission of light in the visible light range. The calculated dielectric functions and absorption spectra demonstrate that the band gap reduction enhances the optical absorption around the 2.5 eV region. Interestingly, the In1-xZnxN1-xOx alloy with x=0.25 has the large optical absorption coefficient in the energy region 0.69-6.0 eV, and the alloy has very good absorption at 2-3 eV.

Place, publisher, year, edition, pages
2012. Vol. 209, no 1, 75-78 p.
Keyword [en]
absorption, band gap, dielectric function, GaN, InN, semiconductor alloys, ZnO
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-95277DOI: 10.1002/pssa.201100148ISI: 000303380700015ScopusID: 2-s2.0-84055218396OAI: diva2:527646
Swedish Research Council
QC 20120522Available from: 2012-05-22 Created: 2012-05-21 Last updated: 2015-04-23Bibliographically approved
In thesis
1. First principles study of oxide semiconductors for solar energy applications
Open this publication in new window or tab >>First principles study of oxide semiconductors for solar energy applications
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objectives of this thesis are to understand the electronic structures of oxides and oxynitrides for photocatalytic water splitting, examine the Casimir interaction between oxides, and explore possible approach to bridge the Casimir force and material properties for advanced material research. The studies were performed in the framework of the density functional theory, many-body perturbation theory, i.e, the GW approximation and Bethe-Salpeter equation, as well as the Casimir-Lifshitz approach.

The thesis consists of two sets of results. In the first part (papers I-VI), the electronic structures of oxynitrides, i.e., ZnO-GaN and ZnO-InN, with different compositions and local structures have been studied. The oxynitrides reduce the band-gap energies significantly compared to the binary counterparts, enabling the oxynitrides to act as visible light active photocatalysts. Formation of cluster--like structures further reduces the band-gap and delocalizes the valence bands, benefiting higher optical absorption. Furthermore, the energy levels between oxynitride and water were aligned using a surface model adapted from semiconductor heterostructure.

In the second part (papers V-IX), the electronic structures of oxides as well as the Casimir interactions have been examined. In particular, we investigated the differences of optical and electronic properties between SnO2 and TiO2 polymorphs in terms of band-edge characters and electron-phonon coupling. In addition, we synthesized a mesoporous material possessing two types of pore structures (one is hexagonal ordered with pore diameter of 2.60 nm and the other is disordered with pore diameter of 3.85 nm). The pore framework contains four-coordinated titanium and oxygen vacancies, verified by both experimental measurements and density-functional theory calculations. Utilizing the predicted properties of the materials, we studied the Casimir interactions. A stable equilibrium of Casimir force is achieved in planar geometry containing a thin film and porous substrates. Both the force and equilibrium distance are tuned through modification of the material properties, for instance, optical properties and porosity. Furthermore, we adapted this concept to study the interactions between gas bubbles and porous SiO2 in water. A transition from repulsion to attraction is predicted, which highlights that the bubbles may interact differently at different surface regions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. viii, 96 p.
photocatalysis; water splitting; oxynitrides; dielectric function; first-principles calculation; density functional theory; electronic structures; Casimir interaction
National Category
Materials Engineering
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-165070 (URN)978-91-7595-451-6 (ISBN)
Public defence
2015-05-22, D3, Lindstedtsvägen 5, KTH, Stockholm, 13:00 (English)

QC 20150423

Available from: 2015-04-23 Created: 2015-04-22 Last updated: 2015-04-23Bibliographically approved

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