The thermo-optical and optical properties of thin ZnO and AZO films produced using the atomic layer deposition technology

In this work, the influence of temperature on the optical constants of zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) thin layers is presented. Thin layers of ZnO and AZO were deposited on silicon using the atomic layer deposition (ALD) method. Optical constants were determined based on ellipsometric measurements in spectral range of 193–1690 nm at temperatures varying from 25° to 300°C. From thermal ellipsometric results, the thermo-optical coefficient (TOC) and thermal expansion coefficient (TEC) have been determined. We have shown that after two cycles of heating and cooling, the thermo-optic processes are reversible. Additionally, complementary studies: XRD, EDS, SEM have been presented. The relationships between the structure of presented films and their optical properties have been discussed. We have shown that the doping of Al to the ZnO matrix changes the sign of the thermo-optical coefficient from negative to positive. The results have been explained based on Prod-Homme theory.