Tailoring the Complex Dielectric Response and Achieving Bandgap Recovery in Single and Double Doped (Mg, Ni, Al) ZnO Thin Films

Abstract

Zinc oxide (ZnO) is a promising wide-bandgap semiconductor, yet isolated doping often induces structural disorder and optical energy dissipation. To address these challenges, this study investigates the structural, morphological, and opto-dielectric dynamics of mono- and co-doped (Mg, Ni, Al) ZnO thin films synthesized via spray pyrolysis. Structural characterization confirmed a stable hexagonal wurtzite lattice, revealing that while single Ni-doping caused excessive grain growth and morphological degradation, introducing synergistic dual-doping (Mg-Ni and Mg-Al) refined the microstructure and significantly enhanced surface homogeneity. By modulating the complex dielectric response governing both optical polarization and energy loss – the co-doping strategy successfully minimized defect-induced scattering, maintaining over 80% visible transmittance. Crucially, the targeted Mg-Ni co-doping effectively counteracted the detrimental band-narrowing caused by isolated Ni-doping, recovering the optical bandgap from 3.17 to 3.22 eV. Furthermore, these double-doping configurations substantially reduced structural disorder, as evidenced by a minimized Urbach energy and a suppressed extinction coefficient. These findings demonstrate that engineering the opto-dielectric properties through comprehensive single and double (Mg, Ni, Al) doping successfully overcomes structural degradation, optimizing the overall integrity of ZnO thin films for advanced optoelectronic and photovoltaic applications.