Atmospheric pressure spatial atomic layer deposition of p-type CuO thin films from copper(ii) acetylacetonate and ozone for UV detection

Cupric oxide (CuO) is a promising p-type semiconducting oxide used in many critical fields, such as energy conversion and storage, and gas sensors, which is attributed to its unique optoelectrical properties and cost-effectiveness. This work successfully deposited amorphous, pinhole-free, ultrathin CuO films using atmospheric pressure spatial atomic layer deposition (SALD) with copper(ii) acetylacetonate and ozone as precursors. The growth rate increased from 0.05 Å/cycle at 175 °C to 0.35 Å per cycle at 275 °C. XPS and XRD confirmed the formation of a pure CuO phase, with typical strong satellite shake-up peaks, and a tenorite crystalline phase. The films exhibited semiconducting behavior, with temperature-dependent electrical measurements revealing the Fermi level positioned 0.2-0.24 eV above the valence band. Furthermore, p-type CuO was combined with n-type ZnO, both deposited by SALD, to form a high-performance photodiode. This CuO/ZnO heterojunction demonstrated excellent rectifying behavior, with an I_ON/I_OFF ratio of 2.04 × 10³, and functioned as an efficient UV detector, showing fast response and good repeatability. These results highlight the potential of SALD-deposited CuO thin films for optoelectronic applications.