Deposition Temperature-Driven Mobility Enhancement in p-Type Transparent Conductive γ-CuI Films Grown by Physical Vapor Transport

High-mobility p-type transparent conductive films (TCFs) are crucial for transparent optoelectronic devices. This work addresses this gap by growing high-quality γ-CuI films on c-Al2O3 substrates via physical vapor transport (PVT), with a focus on the role of deposition temperature. The temperature significantly influences the structural, morphological, optical, and electrical properties of the films. The method delivers an ultrahigh deposition rate of 371 nm/min at 490 °C. The films exhibit (111) out-of-plane orientation and >85% average transmittance (400–800 nm). Structural and morphological analyses reveal temperature-driven growth mode from porous polycrystalline islands to step-flow triangular domains and merged hexagonal structures, which is governed by domain epitaxy. The φ-scan and transmission electron microscopy (TEM) results established the epitaxial relationship as γ-CuI <112̅> (111) // Al2O3 [1̅1̅20] (0001). Electron backscatter diffraction (EBSD) revealed two crystallographic domains that were rotated by 60° relative to each other. The hole mobility increased with deposition temperature, yielding a high hole mobility of 19 cm2/V·s at 490 °C with a carrier concentration of 1.86 × 1017/cm3. These findings indicate that the deposition temperature is critical for achieving high-mobility films. Furthermore, PVT affords a scalable and efficient epitaxy route to p-type transparent conductors, thereby enabling high-performance transparent optoelectronic devices.