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Theoretical investigation of atomic and electronic structures of Ga2O3(ZnO)(6)

Da Silva, JLF; Walsh, A; Wei, SH; (2009) Theoretical investigation of atomic and electronic structures of Ga2O3(ZnO)(6). PHYS REV B , 80 (21) 10.1103/PhysRevB.80.214118.

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Transparent conducting oxides (TCO) are widely used in technological applications ranging from photovoltaics to thin-film transparent field-effect transistors. In this work we report a first-principles investigation, based on density-functional theory, of the atomic and electronic properties of Ga2O3(ZnO)(6) (GZO(6)), which is a promising candidate to be used as host oxide for wide band gap TCO applications. We identify a low-energy configuration for the coherent distribution of the Ga and Zn atoms in the cation positions within the experimentally reported orthorhombic GZO(6) structure. Four Ga atoms are located in four-fold sites, while the remaining 12 Ga atoms in the unit cell form four shared Ga agglomerates (a motif of four atoms). The Zn atoms are distributed in the remaining cation sites with effective coordination numbers from 3.90 to 4.50. Furthermore, we identify the natural formation of twin-boundaries in GZO(6), which can explain the zigzag modulations observed experimentally by high-resolution transmission electron microscopy in GZO(n) (n=9). Due to the intrinsic twin-boundary formation, polarity inversion in the ZnO tetrahedrons is present which is facilitated by the formation of the Ga agglomerates. Our analysis shows that the formation of fourfold Ga sites and Ga agglomerates are stabilized by the electronic octet rule, while the distribution of Ga atoms and the formation of the twin-boundary help alleviate excess strain. Finally we identify that the electronic properties of GZO(6) are essentially determined by the electronic properties of ZnO, i.e., there are slight changes in the band gap and optical absorption properties.

Type: Article
Title: Theoretical investigation of atomic and electronic structures of Ga2O3(ZnO)(6)
DOI: 10.1103/PhysRevB.80.214118
Keywords: ab initio calculations, absorption coefficients, crystal structure, density functional theory, electronic density of states, energy gap, field effect transistors, gallium compounds, photovoltaic cells, thin film transistors, transmission electron microscopy, twin boundaries, wide band gap semiconductors, TRANSPARENT CONDUCTING OXIDES, AUGMENTED-WAVE METHOD, HOMOLOGOUS COMPOUNDS, PHASE-RELATIONSHIPS, OPTICAL-PROPERTIES, CRYSTAL-STRUCTURE, ROOM-TEMPERATURE, THIN-FILMS, SYSTEM, SEMICONDUCTORS
UCL classification: UCL > School of BEAMS > Faculty of Maths and Physical Sciences
UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry
URI: http://discovery.ucl.ac.uk/id/eprint/170277
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