Growth and Optical Parameters of ZnO Films on Macroporous Silicon Obtained by Atomic Layer Deposition

Abstract

The present study is aimed at investigating the process of forming zinc oxide films on macroporous silicon using thermal atomic layer deposition. The macroporous silicon substrate is fabricated by electrochemical etching of a p-type monocrystalline silicon wafer. The ZnO film is deposited at 200°C using diethylzinc (DEZ) and water (H₂O) as precursors. Scanning electron microscopy results confirm uniform coverage of the macroporous silicon surface by the film. Elemental analysis by energy dispersive X-ray spectroscopy shows that the film consists of zinc and oxygen atoms. Raman scattering confirms the structure of the film as the crystalline phase of ZnO. Spectroscopic ellipsometry accurately determined with high precision the film thickness at 46 nm and the surface roughness at 4 nm. In addition, the optical properties of the film, including absorption coefficient, refractive index, and optical bandgap, are investigated. The results indicate a high transparency of the ZnO film in the visible spectrum and its ability to absorb ultraviolet radiation. The optical bandgap of 3.28 eV, Urbach tail in the absorption spectrum, and the detected roughness on the film surface indicate its polycrystalline nature and inhomogeneous crystal growth. The results show that ZnO films obtained by thermal atomic layer deposition can be used as transparent conducting electrodes in photoconverters due to their high transparency in the visible range. In addition, this method has the potential to create finely tunable ZnO/porous Si heterostructures with a large specific surface area.