Influence of stoichiometry on defect formation and electrical transport properties of DC sputtered Cu3N thin films

Copper nitride (Cu 3 N) is a narrow band gap semiconductor with promising electrical properties suitable for many emerging applications. However, achieving the desired semiconducting properties remains challenging due to its metastable nature. A small variation in the stoichiometry can introduce native point defects such as copper interstitials (Cu i ) and copper vacancies (V C u ), which dramatically alter the electrical transport properties and determine the type of conductivity. This work investigates the crucial role of stoichiometry in regulating defect formation and electrical transport behaviour in sputtered Cu 3 N thin films, by systematically varying the nitrogen flow ratio during deposition from 50% to 75%. X-ray diffraction reveals a distinct change in the preferred crystallographic orientation from (111) to (100) planes as nitrogen flow ratio increases, accompanied by morphological transformations from compact pyramidal cone grains to flower-like and triangular shaped grains, as observed through scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) provides direct evidence of the defect transition from Cu i in nitrogen deficient conditions to V C u in nitrogen rich conditions, manifested as systematic shifts in Cu 2p binding energies and valence band spectra. Hall effect analysis reveals that nitrogen-rich deposition conditions suppress the carrier concentration and increase resistivity. The nitrogen deficient conditions films exhibit enhanced n-type conductivity driven by Cu i defects, whereas the resistivity decreases with an increased carrier concentration. Temperature dependent resistivity measurements spanning 80–350 K reveal variable range hopping conduction, indicating that electron transport proceeds via hopping between localized states in the defect lattice. A long-term stability analysis was conducted over 1 year under ambient conditions, demonstrating that films deposited under nitrogen-rich conditions were possibly susceptible to surface oxidation. These results establish a quantitative relationship between stoichiometry, defect chemistry, and electrical transport properties, offering a systematic approach to tailor Cu 3 N thin films for applications in resistive memory switching, thermoelectric devices, and gas sensors. • Stoichiometry of sputtered Cu 3 N determines defect chemistry and electrical properties. • Nitrogen flow drives a defect transition from copper interstitials to copper vacancies. • Temperature dependent resistivity shows variable range hopping conduction. • One-year ambient tests reveal nitrogen-rich Cu 3 N films are prone to surface oxidation.