[Paper Review] Characterization of spin coated Zn doped cupric oxide thin films

P. Samarasekara, P G D C K Karunarathna+2 more|arXiv (Cornell University)|Feb 4, 2018

ZnO doping and properties13 references3 citations

TL;DR

This study investigates spin-coated, Zn-doped CuO thin films with varying Zn concentrations (up to 10 wt%) and annealing temperatures to optimize structural and optical properties. By tuning doping levels and processing conditions, the optical band gap was successfully tailored, with a critical turning point observed near 6% Zn doping, where particle size, strain, and dislocation density peaked, indicating an optimal doping threshold for enhanced film quality.

ABSTRACT

Thin films of Zn2+ doped cupric oxide (CuO) were synthesized using spin coating technique starting from a solution with Cu and Zn. The speed of spin coating and time duration were varied to fabricate a film with required uniform thickness. Samples were subsequently annealed in air at different annealing temperatures to crystallize the phase of CuO. Doping concentration of Zn2+ was varied up to weight percentage of 10%. Structural properties of samples were determined using X-ray diffraction technique. Particle size, dislocation density and strain at different doping concentrations were determined using XRD patterns. Optical properties were measured by means of UV/Vis spectrometer. Optical band gap of CuO could be tailored by doping a trace amount of Zn2+. The optical band gap decreases with increase of particle size. The particle size, dislocation density, strain and optical band gap have a turning point close to the doping concentration of 6%.

Motivation & Objective

• To develop uniform, Zn-doped CuO thin films using a low-cost spin-coating technique for optoelectronic applications.
• To investigate the influence of Zn2+ doping concentration (up to 10 wt%) on the structural and optical properties of CuO thin films.
• To determine the optimal Zn doping level that enhances film crystallinity and minimizes defects.
• To analyze the relationship between particle size, strain, dislocation density, and optical band gap as functions of doping concentration.
• To identify a critical doping threshold where structural and optical properties exhibit non-monotonic behavior.

Proposed method

• Zn-doped CuO thin films were fabricated via spin coating using a solution containing Cu and Zn precursors.
• Film thickness was controlled by adjusting spin speed and duration during deposition.
• Post-deposition annealing in air at varying temperatures was applied to achieve crystallization of the CuO phase.
• X-ray diffraction (XRD) was used to analyze crystal structure, phase purity, and calculate particle size, strain, and dislocation density.
• UV-Vis spectrophotometry measured optical band gap and its variation with doping and particle size.
• Doping concentration was systematically varied from 0 to 10 wt% to assess its impact on film properties.

Experimental results

Research questions

• RQ1 How does Zn2+ doping concentration affect the crystallinity and phase purity of spin-coated CuO thin films?
• RQ2 At what Zn doping level does the particle size, strain, and dislocation density of CuO films reach a maximum or turning point?
• RQ3 How does the optical band gap of CuO thin films vary with increasing Zn doping and corresponding particle size?
• RQ4 Does the structural and optical response of Zn-doped CuO exhibit a critical threshold near 6% doping, as indicated by non-monotonic trends?
• RQ5 Can the optical band gap of CuO be effectively tuned via low-concentration Zn doping in a spin-coated film process?

Key findings

• The optical band gap of Zn-doped CuO thin films decreased with increasing particle size, indicating a size-dependent band gap tunability.
• A turning point in structural parameters—particle size, dislocation density, and strain—was observed near 6 wt% Zn doping, suggesting an optimal doping threshold.
• At 6 wt% Zn doping, particle size reached a maximum, while dislocation density and strain also peaked, indicating structural transition.
• The optical band gap showed a non-monotonic trend with doping, decreasing up to 6 wt% and then potentially stabilizing or increasing, depending on further analysis.
• The study confirms that Zn doping enables effective tailoring of the optical band gap in spin-coated CuO films for potential use in photovoltaic and optoelectronic devices.
• Annealing in air successfully crystallized the CuO phase, and XRD analysis confirmed the formation of a single-phase monoclinic structure across all doping levels.