Tuning the optical bandgap in multi-cation compound transparent conducting-oxides: The examples of In2ZnO4 and In4Sn3O12

Author(s)

Sabino, Fernando P. ^{[1, 2]} ; Oliveira, Luiz N. ^[1] ; Wei, Su-Huai ^[3] ; Da Silva, Juarez L. F. ^[4]

Affiliation

^[1] Univ Sao Paulo, Sao Carlos Inst Phys, POB 369, BR-13560970 Sao Carlos, SP - Brazil

^[2] Univ Delaware, Dept Mat Sci & Engn, Newark, DE 19716 - USA

^[3] Beijing Computat Sci Res Ctr, Beijing 100094 - Peoples R China

^[4] Univ Sao Paulo, Sao Carlos Inst Chem, POB 780, BR-13560970 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: Journal of Applied Physics; v. 123, n. 5 FEB 7 2018.
• Web of Science Citations: 0

Abstract

Transparent conducting oxides such as the bixbyite In2O3 and rutile SnO2 systems have large disparities between the optical and fundamental bandgaps, Delta E-g(OF), because selection rules forbid dipolar transitions from the top of the valence band to the conduction-band minimum; however, the optical gaps of multi-cation compounds with the same chemical species often coincide with their fundamental gaps. To explain this conundrum, we have employed density-functional theory to compute the optical properties of multi-cation compounds, In2ZnO4 and In4Sn3O12, in several crystal structures. We show that a recently proposed mechanism to explain the disparity between the optical and fundamental gaps of M2O3 (M = Al, Ga, and In) applies also to other binary systems and to multi-compounds. Namely, a gap disparity will arise if the following three conditions are satisfied: (i) the crystal structure has inversion symmetry; (ii) the conduction-band minimum is formed by the cation and O s-orbitals; and (iii) there is strong p-d coupling and weak p-p in the vicinity of the valence-band maximum. The third property depends critically on the cationic chemical species. In the structures with inversion symmetry, Zn (Sn) strengthens (weakens) the p-d coupling in In2ZnO4 (In4Sn3O12), enhancing (reducing) the gap disparity. Furthermore, we have also identified a In4Sn3O12 structure that is 31.80 meV per formula unit more stable than a recently proposed alternative model. Published by AIP Publishing. (AU)

• FAPESP's process: 13/21045-2 - Theoretical prediction of the structure, thermodynamic stability, electronic, and reactivity properties of nanoclusters
• Grantee: Juarez Lopes Ferreira da Silva
• Support Opportunities: Regular Research Grants