Controlling Compensation Doping via Multivalent Platinum Acceptors in Tantalum Oxide Thin Films

Heterostructures of platinum (Pt) and tantalum oxide (Ta2O5) find widespread use in electronic and energy-conversion device applications, yet the electronic role of Pt incorporated within Ta2O5 remains poorly understood. Here, we investigate the influence of Pt incorporation on the electronic structure and properties of amorphous Ta2O5 using two precisely controlled ternary atomic layer deposition (ALD) pathways. Oxygen plasma-enhanced deposition produces host matrices with significantly lower native defect and impurity concentrations than conventional thermal water-based ALD, enabling a systematic investigation of the interplay between Pt dopants and native defects. Controlled Pt incorporation over the range of 0.9-1.9 atom % yields homogeneous, amorphous Pt-doped Ta2O5 thin films containing exclusively Pt(II) and Pt(IV) oxidation states, with no evidence of metallic Pt formation. While the optical bandgap of the Ta2O5 host matrix remains largely unchanged, Pt incorporation introduces optically active acceptor states near the valence band maximum, increases sub-bandgap absorption, and shifts the Fermi level toward the midgap. The relative Pt(II)/Pt(IV) population depends strongly on the defect landscape of the host matrix and exhibits a linear dependence on the Fermi level position, demonstrating Fermi level-controlled charge compensation between native donor defects and multivalent Pt acceptor states. Density functional theory corroborates the acceptor character of Pt and assigns the introduced states primarily to Pt 5d orbitals. Experimentally constructed band diagrams and charge transport measurements further show that Pt incorporation provides a direct means of tuning the electronic properties of Ta2O5. These results demonstrate that multivalent Pt doping serves as a controllable strategy for engineering the electronic structure and transport characteristics of functional Ta2O5 thin films, with direct relevance to memristive, dielectric, and photoelectrochemical devices.