Effects of Passivation Layer and Post-Annealing on Ga-Doped ZnO Films Grown by ALD

In this study, we investigate the effects of passivation layer and post-annealing on the Ga-doped ZnO films grown by thermal-mode atomic layer deposition (TM-ALD) with using H2O as oxidant source. The resistivity of ALD-grown GZO deposited on glass and sapphire substrates are 3.9 × 10−4 Ω-cm and 3.7 × 10−4 Ω-cm, respectively. The resistivity of GZO films rises irresistibly after post-annealing, especially in oxygen atmosphere. The resistivity also has a significant dependence of substrate and post-annealing ambient. Deposition of a passivation layer is effective to keep the low resistivity and high carrier concentration of GZO during post-annealing due to the preservation of the oxygen vacancies. The resistivity could be kept at 6.7 × 10−4 Ω-cm even by post-annealing at 700°C. The lowest resistivity of GZO on sapphire substrates is 3.3 × 10−4 Ω-cm by capping SiO2 and 3.29 × 10−4 Ω-cm by capping Al2O3 at 400°C post-annealing. The maximum transmittance of as-grown GZO increases with post-annealing temperature, especially in the long-wavelength range. In addition, the transmittance in the visible range can be enhanced without red-shift after post-annealing by using a passivation layer.