Contact engineering of p-type CuI thin films: Interplay of work function alignment and interfacial chemical stability

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Original abstract

Abstract Copper iodide (CuI) is a promising p-type transparent conductors, yet its device application is limited by poorly understood contact properties. This study systematically investigates Pt, W, Mo, and Ag contacts on CuI thin films using transmission line method structures. Classical band theory predicts ohmic contact only for metals with work functions exceeding that of CuI (~5.1 eV). Experimentally, Pt (5.6 eV) shows an excellent ohmic contact with a low specific contact resistance of 60 Ω, as expected. Surprisingly, Mo (4.6 eV) and W (4.5 eV) also form low-resistance ohmic contacts despite their lower work functions. This is due to the high hole concentration (~10 19 cm -3 ) in CuI, which narrows the depletion width and enables efficient hole tunneling. In contrast, Ag (4.3 eV) forms a rectifying contact but exhibits anomalous nanoampere-level current and hysteresis, arising from severe interfacial iodization. Cross-sectional analysis confirms that while Pt, Mo, and W interfaces are sharp and stable, Ag reacts with iodine, forming a diffused interlayer. The contact performance is improved by thermal annealing at 100-200 ℃. This work establishes that alongside work function alignment, chemical stability against iodization is a critical criterion for selecting electrodes in CuI-based devices.

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