Structural, electrical, and optical properties of Ti-doped ZnO films fabricated by atomic layer deposition

High-quality Ti-doped ZnO films were grown on Si, thermally grown SiO2, and quartz substrates by atomic layer deposition (ALD) at 200°C with various Ti doping concentrations. Titanium isopropoxide, diethyl zinc, and deionized water were sources for Ti, Zn, and O, respectively. The Ti doping was then achieved by growing ZnO and TiO2 alternately. A hampered growth mode of ZnO on TiO2 layer was confirmed by comparing the thicknesses measured by spectroscopic ellipsometry with the expected. It was also found that the locations of the (100) diffraction peaks shift towards lower diffraction angles as Ti concentration increased. For all samples, optical transmittance over 80% was obtained in the visible region. The sample with ALD cycle ratio of ZnO/TiO2 being 20 had the lowest resistivity of 8.874 × 10-4 Ω cm. In addition, carrier concentration of the prepared films underwent an evident increase and then decreased with the increase of Ti doping concentration.