Electrical Tuning and Enhanced UV Detection Capabilities in Zn-Doped CuI Thin Films

The development of heterostructures has emerged as a key area in advancing next-generation electronic devices, which draws substantial attention within the research community. In this work, copper iodide (CuI)/silicon heterojunctions were fabricated using the horizontal thermal evaporation (TE) technique, with systematic incorporation of zinc ions (Zn2+) to modulate the structural and electronic behavior of the CuI thin films. A detailed investigation was conducted to examine the influence of varying Zn2+ doping concentrations on the structural, morphological, optical, and electrical properties of the films. X-ray diffraction (XRD) analysis revealed the polycrystalline nature of the CuI films, with shifting of (111) diffraction peaks towards higher 2θ values. Raman spectra consistently exhibited a peak shift to higher wavenumbers at 125 cm–1 with increasing Zn2+ content, indicating enhanced bond stiffness and stronger vibrational modes. Photoluminescence (PL) studies revealed that the evolution of an intense emission peak around 410 nm for films doped with 1 mol % Zn2+. Elemental analysis via energy-dispersive X-ray spectroscopy (EDX) attributed the presence of Zn in the films over the entire doping range of 0.5 to 2.5 mol %, including Cu and I. Surface morphology investigations indicated a notable increase in surface roughness, from approximately 1 nm in undoped films to about 7 nm at higher Zn2+ doping levels. Hall effect measurements have shown an increase in carrier concentration with Zn2+ doping, with a clear transition to n-type conductivity observed up to 1.5 mol % Zn2+. The electron concentration has been achieved as 1.38 × 1018 cm–3 for 2.5 mol %. Under 365 nm illumination, current–voltage (I–V) studies depict enhanced photoresponse at 1 mol % Zn2+, which is attributed to more effective ultraviolet (UV) light absorption and charge transport. Here, the lowest forward turn-on voltage (VF) is measured to be 0.40 V. In this work, the incorporation of Zn2+ greatly enhances the photoresponse characteristics of CuI-based photodetectors, which opens a new possibility for the development of next-generation, high-performance photodetection devices.