Suppression of Grain Boundary Scattering in Multifunctional p-Type Transparent γ-CuI Thin Films due to Interface Tunneling Currents

Transparent p-type conductive γ-CuI thin films typically exhibit unexpectedly high hole mobilities in the range of 10 cm² V⁻¹ s⁻¹ even when heavily textured. To explain this phenomenon, the transport properties of such thin films are investigated. The temperature-dependent resistivities of the textured (111)-oriented films with different carrier concentration are fitted using the fluctuation-induced tunneling conductivity (FITC) model in series with a power law. The FITC model describes barriers at the grain boundaries whereas the power law considers the scattering in the metallic interior of the grains. Magnetoresistance measurements performed on a reactively DC-sputtered thin film at low temperatures (T < 8 K) suggest a 2D weak antilocalization effect with phase coherence lengths of about 50 nm. This is corroborated by a typical logarithmic temperature dependence of the zero-field conductance. An n-type inversion layer or a defect band at the interfaces of the grains as origin of the 2D carrier system and the barriers at the grain boundaries is proposed. This leads to a conclusive description of the electrical transport properties of γ-CuI thin films and explains the high hole mobilities which are due to a suppressed backscattering at the grain boundaries in the presence of tunneling channels.