Structural, electrical, and optical properties of Si-doped ZnO thin films prepared via supercycled atomic layer deposition

Si-doped zinc oxide (ZnO) thin films were fabricated via atomic layer deposition (ALD) using diethylzinc, Tris(dimethylamino)silane, and H₂O as Zn, Si, and O sources, respectively. The ALD cycle of the (Zn-O) step and the (Zn-Si-O) step were separated and the Si concentration was controlled via changing the (Zn-Si-O) pulse cycle compared to the (Zn-O) step. This Si source pulse sequence (Zn-Si-O) is different from the conventional (O-Si) pulse sequence and was specially selected in this study to maximize the properties of the thin film. All of the films showed the hexagonal wurtzite structure of ZnO with the (1 0 0) plane producing the main diffraction peak when ALD was performed at 200 ℃. As the Si-doping concentration increased, the crystallinity of the films deteriorated and the Scherrer size was reduced from 29.69 to 28.10 nm, there were improvements in the electrical characteristics, the carrier concentration increased up to 8.10 × 10²⁰ cm⁻³, and the resistivity decreased to 5.15 × 10^-4 Ω·cm, which is lower than the lowest previously reported result for Si-ZnO thin films fabricated via ALD (9.29 × 10^-4 Ω·cm). Moreover, the carrier mobility increased at first (Si-ZnO 1:29 supercycles) and then decreased with increasing Si concentration. The average transmittance of all of the films was above 80% and the optical band gap increased from 3.29 to 3.47 eV. The increased carrier concentration according to the Burstein-Moss effect was linearly related to the band gap shift while up-shifting the E_F (Fermi level) toward the conduction band. We expect that our approach in this study will provide an experimental basis to optimize ZnO thin-film characteristics via modification of Si pulsing sequence.