Double-Hole-Mediated Coupling of Dopants and Its Impact on Band Gap Engineering in ${\mathrm{TiO}}_{2}$

Double-Hole-Mediated Coupling of Dopants and Its Impact on Band Gap Engineering in ${TiO}_{2}$

Wan-Jian Yin, Su-Huai Wei, Mowafak M. Al-Jassim, and Yanfa Yan

Phys. Rev. Lett. 106, 066801 – Published 10 February 2011

Abstract

A double-hole-mediated coupling of dopants is unraveled and confirmed in ${TiO}_{2}$ by density-functional theory calculations. We find that when a dopant complex on neighboring oxygen sites in ${TiO}_{2}$ has net two holes, the holes will strongly couple to each other through significant lattice relaxation. The coupling results in the formation of fully filled impurity bands lying above the valence band of ${TiO}_{2}$ , leading to a much more effective band gap reduction than that induced by monodoping or conventional donor-acceptor codoping. Our results suggest a new path for semiconductor band gap engineering.