Enhanced infrared transmittance by modulation of electrical and optical properties of Sm-doped SnO₂ thin films

Although metal oxides exhibit high electrical conductivity and high transparency in the visible wavelength range, they suffer from low transmittance in the infrared (IR) spectral range. This paper reports the deposition of Sm-doped SnO₂ thin films with high IR transparency by modulating the electrical and optical properties. The Sm-doped SnO₂ thin films grown by spray pyrolysis showed a directional columnar structure and a change in crystal structure from tetragonal to orthorhombic with increasing Sm doping content. The undoped SnO₂ thin film exhibited intrinsic n-type conductivity with a high background charge carrier concentration, which resulted in low IR transmittance of <20%. As the Sm doping content increased, the charge carrier concentration decreased drastically, resulting in an increase in IR transmittance of SnO₂ thin films from 18.8 to 85.2%. The Sm element acted a critical role in controlling the electrical and optical properties of SnO₂ thin films by acting as a reducing agent and dopant.