Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from In₂O₃

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In₂O₃), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chemical properties of the contact layers and the interface region toward In₂O₃, to analyze charge transfer and plasma oxidation processes as well as to evaluate the precision and limits of different methodologies to determine heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissolution of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In₂O₃ electron concentration of ∼10¹⁸ cm^-3. A reactive sputter process in an Ar and O atmosphere is required to fabricate rectifying contacts that are composed of platinum oxide (PtO). Combining oxygen plasma interface oxidation of the semiconductor surface with reactive sputtering of PtO layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 10⁶. An additional oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.