Nanostructured α-Fe₂O₃ Photoelectrodes with Transparent and Conducting Sb-Doped SnO₂ Films Deposited by Atomic Layer Deposition

Antimony (Sb)-doped tin oxide (ATO), as a transparent conducting oxide, is successfully deposited through atomic layer deposition (ALD). Thin films (≈270 nm) with various dopant concentrations are fabricated by sequential mixing of Sn- and Sb-containing oxide layers in each ALD supercycle. The crystal structure, chemical composition, and morphologies of different films are characterized. Increasing the dopant concentration decreases the lattice parameter along the c-axis and the overall grain size, as observed from X-ray diffraction patterns and scanning electron microscopy images. X-ray photoelectron spectroscopy spectra show increasing Sb content with increasing Sb to Sn subcycle ratio. The plasmonic loss feature, which is usually observed in highly doped degenerate semiconductors, is also found. Hall measurements are carried out to determine the electrical properties of each film, and films with ≈5% dopant concentration show the optimal conductivity. The carrier concentration continues to increase with increasing dopant concentration in the range of 0–20%, while the mobility decreases, which leads to a trade-off and results in an increase in resistance if the dopant concentration exceeds 5%. The optimized ATO ALD process is demonstrated to fabricate core–shell structured nanotube arrays, which show its potential usage for photoelectrochemical applications.