Autor(es)

Sabino, Fernando P. ; Besse, Rafael ; Oliveira, Luiz Nunes ; Wei, Su-Huai ; Da Silva, Juarez L. F.

• Tipo de documento: Artigo Científico
• Fonte: Physical Review B; v. 92, n. 20, p. 7-pg., 2015-11-23.

Resumo

Good transparent conducting oxides (TCOs), such as In2O3:Sn (ITO), usually combine large optical band gaps, essential for high transparency, with relatively small fundamental band gaps due to low conduction-band minima, which favor n-type doping and enhance the electrical conductivity. It has been understood that the optical band gaps are wider than the fundamental band gaps because optical transitions between the band-edge states are forbidden. The mechanism blocking such transitions, which can play a crucial role in the designing of alternative TCOs, nonetheless remains obscure. Here, based on first-principles density functional theory calculations and symmetry analysis of three oxides, M2O3 (M = Al, Ga, In), we identify the physical origin of the gap disparities. Three conditions are necessary: (1) the crystal structure must have global inversion symmetry; (2) in order to belong to the A(g) or A(1g) irreducible representations, the states at the conduction-band minimum must have cation and oxygen s character; (3) in order to have g parity, the oxygen p orbitals constituting the states near the valence-band maximum must be strongly coupled to the cation d orbitals. Under these conditions, optical excitations across the fundamental gap will be forbidden. The three criteria explain the trends in the M2O3 (M = Al, Ga, In) sequence, in particular, explaining why In2O3 in the bixbyite structure yields the highest figure of merit. Our study provides guidelines expected to be instrumental in the search for new TCO materials. (AU)

• Processo FAPESP: 13/21045-2 - Predição teórica da estrutura, estabilidade termodinâmica, propriedades electronicas e reatividade de nanoclusters
• Beneficiário: Juarez Lopes Ferreira da Silva
• Modalidade de apoio: Auxílio à Pesquisa - Regular