Disorder-controlled charge transport and thermistor performance in Cu-doped β-In2S3 thin films for thermal sensing application

Abstract

In this work, Cu-doped β-In 2 S 3 thin films with Cu concentrations of 0%, 4%, 6%, and 8% were deposited by vacuum thermal evaporation, and their structural, microstructural, electrical transport, and thermistor properties were systematically investigated. The primary objective is to elucidate the influence of Cu doping on charge carrier dynamics across both DC and AC conduction regimes and to correlate these mechanisms with thermistor performance. X-ray diffraction (XRD) analysis confirms the formation of single-phase β-In 2 S 3 for all films, demonstrating successful Cu incorporation without secondary phase formation. Energy-dispersive X-ray (EDX) analysis further validates the compositional homogeneity of the films. The effects of Cu doping on charge transport behavior were examined through DC and AC conductivity measurements over a wide temperature range. DC electrical measurements reveal semiconducting behavior governed by thermally activated charge transport, with activation energies indicating enhanced carrier localization upon Cu incorporation. The conduction mechanisms were analyzed using small polaron hopping, Greaves hopping, and Mott variable-range hopping models, providing a comprehensive description of the transport processes in different temperature regimes. Frequency-dependent AC conductivity spectra exhibit distinct dispersive regions, and the temperature dependence of the frequency exponent supports the applicability of the Quantum Mechanical Tunneling for the undoped β-In 2 S 3 and the Nearly Constant Loss model for the doped films. Scaling analysis reveals successful superposition of conductivity spectra for all compositions, confirming the validity of the time-temperature superposition principle, while Summerfield scaling indicates weak Coulomb interactions and temperature-independent microscopic dynamics. Key thermistor parameters, including maximum temperature coefficient of resistance, thermistor constant β, sensitivity factor α, and stability factor, were extracted and show systematic enhancement with increasing Cu content. These results establish a direct correlation between Cu- induced modifications in charge carrier dynamics and improved thermistor performance. This work provides new insight into the interplay between doping, transport mechanisms, and sensing properties in β-In 2 S 3 thin films, highlighting their potential for high-temperature thermistor applications.