Nanocrystalline ZnO Films on Various Substrates: A Study on Their Structural, Optical, and Electrical Characteristics

Abstract

Zinc oxide (ZnO), characterized by its wide bandgap and substantial exciton binding energy, is extensively utilized in optoelectronic applications, including blue and ultraviolet light-emitting diodes (LEDs) and lasers. In this study, the deposition of ZnO films on various substrates (Si, sapphire, GaAs, GaP) through thermal oxidation is investigated as a cost-effective alternative to molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). A thorough analysis of the structural, optical, and electrical properties of these films is presented, with a focus on their suitability for heterojunction diodes. The methodology employed involved the thermal evaporation of Zn films in a vacuum chamber, followed by oxidation in a pure oxygen atmosphere. The conditions for deposition were optimized to yield nanocrystalline ZnO films with a preferential orientation, as confirmed by X-ray diffraction (XRD) analysis. An increase in the optical bandgap was indicated by optical transmittance measurements, while photoluminescence (PL) spectra exhibited uniform and enhanced crystalline integrity across the samples. The electrical characterization of ZnO-based heterojunction diodes on different substrates revealed distinct electrical characteristics, with variations in leakage current and ideality factor observed. The specific resistances of the Zinc Oxide (ZnO) films were determined by analyzing the linear portions of the current-voltage (I-V) curves.