Ga acceptor defects in SnO2 revisited: A hybrid functional study

SnO2 is one of the most interesting oxide semiconductors due to its wide band gap, good transparency, high thermal/chemical resistances, and low cost. As-grown SnO2 usually exhibits n-type conductivity with high carrier concentrations. Similar to the case of ZnO, it is difficult to dope SnO2 into p-type. Consequently, applications of SnO2 for optoelectronic as well as electronic devices are limited. In principle, substitution of group-III elements, including Al, Ga, and In, for Sn atom in SnO2 could give a hole carrier resulting in a p-type conductivity. Based on the HSE functional calculations (Varley et al., 2009) [13], it has been reported that these dopants are shallow acceptor defects. However, the calculations with PBE0 functional (Scanlon and Watson, 2012) [14] showed that these dopants are deep acceptors. In this work, Ga-doped SnO2 are revisited by using HSE functional. We found that GaSn defect is indeed a deep acceptor indicating that GaSn can serve only as a compensating acceptor defect in SnO2. Hoping to make the acceptor level shallower, we further study the effect of (compressive) strain on the acceptor level associated with GaSn defect by alloying SnO2 with Si atoms (SixSn1−xO2 alloy where x ~ 0.17). Our results showed that even with the application of strain, the acceptor level remains too deep to be useful.