Low-temperature atomic layer deposition of oriented ZnO thin films on c-plane Al2O3: influence of precursor ratio and growth temperature

Abstract

In this work, ZnO thin films were deposited on c-plane Al₂O₃ substrates by atomic layer deposition (ALD) under various growth conditions. The Zn/O feeding time ratios were adjusted from 0.5 to 3.5 at growth temperatures between 120 °C and 300 °C. Films grown at a temperature (T_g) of 200 °C exhibited superior crystallinity and pronounced (200) orientation compared to those grown at lower temperatures, as increased thermal energy promoted more effective surface diffusion and improved atomic arrangement. Raman and photoluminescence analyses revealed well-defined phonon modes and enhanced near-band-edge ultraviolet emission for the film grown at 200 °C with a Zn/O feeding time ratio of 1.5:2, indicating a high degree of structural uniformity and efficient radiative recombination. These findings elucidate how growth temperature and precursor stoichiometry govern the structural and optical quality of ALD-grown ZnO thin films, underscoring the potential of low-temperature ALD for producing high-quality ZnO layers suitable for semiconductor and optoelectronic device applications.