Atomic layer deposition of Ti-doped ZnO films with enhanced electron mobility

Ti is introduced as a dopant during the atomic layer deposition (ALD) growth of ZnO for use as a transparent electrode. ALD-grown Ti-doped ZnO (TZO) films are deposited via alternate stacking of ZnO and TiO_x atomic-doping layers. Their growth behavior, structural, electrical and optical properties are investigated. Macroscopic film growth and doping concentration characterization show that both diethylzinc and titanium tetrakis(isopropoxide) exhibit enhanced adsorption during the ALD of TZO films. Contrary to conventional homogeneous compounds, atomic-layer Ti doping by ALD results in a much higher electrical conductivity and doping efficiency compared to its Al counterpart. Specifically, the ALD-grown TZO films show an electrical conductivity of 951 S cm⁻¹, nearly twice that of AZO films (591 S cm⁻¹), thanks to the high doping efficiency of Ti (41%) and its extraordinary high mobility (>20 cm² V⁻¹ s⁻¹). Such high electron mobility is likely due to a smaller concentration of inactivated dopants as scattering centers.