Optical and fundamental band gaps disparity in transparent conducting oxides: new findings for the In2O3 and SnO2 systems

Author(s)

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

• Document type: Journal article
• Source: JOURNAL OF PHYSICS-CONDENSED MATTER; v. 29, n. 8 MAR 1 2017.
• Web of Science Citations: 6

Abstract

The optical band gap, extracted from absorption measurements, defines the figure of merit for transparent conducting oxides (TCOs). In many oxides, such as In2O3 or SnO2, inversion symmetry introduces a selection rule that blocks transitions from the valence-band maximum to the conduction-band minimum. This raises the absorption threshold and enlarges the optical gap relative to the fundamental band gap. Here, we present density-functional computations identifying two optical gaps, either of which can be detected, depending on the optical light intensity. Under strong illumination, weak transitions from k-points near the valence-band maximum contribute significantly to the absorption spectrum and define an optical gap matching the fundamental gap. Low optical intensities by contrast give prominence to the large optical gap determined by the selection rule. While experimental conditions have favored observation of the former optical gap in SnO2, in contrast, absorption measurements in In2O3 have focused on the latter. Our findings explain the disparity between the optical and fundamental gaps in bixbyite In2O3 and predict that, measured under low illumination, the optical gap for rutile SnO2 will increase, from 3.60 eV to 4.34 eV. (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