Exploring the morphological and optical properties of N-doped ZnO heterojunctions

Abstract

Nitrogen-doped zinc oxide (N:ZnO) thin films were deposited on glass substrates via radio frequency (RF) magnetron sputtering and subsequently annealed at 300 °C, 400 °C, 500 °C, and 600 °C to assess their viability and stability as transparent conductive oxide (TCO) materials. Structural and compositional analyses were performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). XRD analysis revealed preferential crystallite orientations along the (100), (002), (101), and (110) planes. Atomic force microscopy (AFM) measurements indicated particle sizes two to four times larger than those derived from XRD, suggesting a sub-granular internal structure, as XRD probes coherently diffracting domains. XPS analysis of the N 1 s spectra identified two distinct peaks at approximately 397 eV and 407.5 eV, indicating nitrogen incorporation into the ZnO matrix. Photoluminescence spectroscopy revealed that nitrogen doping induced the formation of interstitials and defects associated with oxygen and zinc vacancies. Optical measurements showed that the (N:ZnO) thin films exhibited an average optical band gap of approximately 3.1 eV, with 80% transmittance in the visible spectrum. A linear relationship was observed between the band gap energy and the tail width. Except for the film annealed at 600 °C, all annealed films showed a reduction in peak photoluminescence intensity with increasing annealing temperature. Finally, no significant changes in the electrical performance of the p-N/n-Si diode were observed as a result of annealing-induced surface modifications. The results provide valuable insights into the optimization of (N:ZnO) thin films for use in international optoelectronic and photovoltaic research, where advancements in TCOs are critical for the development of high-performance, sustainable technologies.