Tunable Transparent Conductors Based on SnO₂: Theoretical and Experimental Studies of Codoping

Transparent conducting oxides (TCOs) are widely used in modern electronics because they have both high transmittance and good conductivity, which is beneficial for many applications such as light-emitting diodes. Tailoring electronic states and hence the conductive types by design is important for developing new materials with optimal properties for TCOs. SnO₂, with a wide band gap, low cost, no toxins, and high stability, is a promising host material for TCOs. Here, we performed a set of hybrid-exchange density functional theory calculations on the two-element and three-element codoped SnO₂ by using Sr, Ta, Al, Ga, V, and Nb, which were then validated by the relevant experimental works on SnO₂. As predicted by the first-principles calculations, the controllability of the electronic states to be n- or p-type can be demonstrated experimentally by varying the relative doping concentration between donors (Ta/Nb) and acceptors (Al/Ga). One of the main advantages for these codoping methods is that the charge neutrality problem caused by the dopant can be circumvented. The thin films fabricated showed a low sheet resistance (down to ∼450 Ω/□) and a high optical transparency (above 80%). The combination of our calculations and experimental material fabrication and characterizations has shown a great potential for codoping SnO₂ for (i) the efficient processing of the integrated circuit composed of both p-type and n-type transistors (using the same target precursors during the deposition) and (ii) a good lattice matching for p-n junctions. Most importantly, our calculations, supported by the experimental works, point to a promising route to accelerate the discovery process for the alternative cost-effective and high-performance indium-free TCOs using computational material design.