Boltzmann conductivity approach for charge transport in spray-deposited transparent Ta-doped SnO2 thin films

Transparent conducting oxide (TCO) thin films should possess good resistance stability with temperature, apart from high figure of merit, to be suitable as electrodes for several potential optoelectronic device applications. In most of the metal oxide systems, an increase in the electrical conductivity with temperature indicates semiconducting behavior up to a certain critical temperature; and above this critical temperature, metal-like behavior is witnessed. Theoretical and experimental evidence for such change in charge transport behavior is crucial for further development and applicability of these TCO systems. In the present work, temperature-dependent electrical properties of spray-pyrolyzed Ta-doped SnO2 (TTO) thin films are explored for their resistance behavior in the high temperature regime. In order to justify the experimentally determined electrical conductivity of the TTO films, the values are correlated with theoretically estimated electrical parameters by adopting Boltzmann conductivity approach. The structural, chemical, morphological, optical and electrical properties of the TTO films indicate the optimal Ta dopant concentration to be 4 wt%. The film deposited with 4 wt% Ta dopant exhibits sheet resistance of 17.96 Ω/□, resistivity of 4.36 × 10−4 Ω cm, transmittance ≅ 85% (at λ = 550 nm) and band gap of 4.01 eV, indicating its potential to serve as wide band gap TCO electrode in several optoelectronic applications.