Characterization of RF magnetron sputtered pure and aluminum-doped zinc oxide thin films for optoelectronic applications

Transparent conductive oxides face critical challenges in simultaneously optimizing electrical conductivity and optical transparency for advanced optoelectronic applications. Zinc oxide (ZnO) and aluminum-doped zinc oxide (Al-ZnO) thin films are extensively studied for their optoelectronic applications due to their excellent transparency (> 85% in visible region) and electrical conductivity. This study presents novel advancements in controlling structural and optical properties through Al doping (0-3 at.%) via RF magnetron sputtering, demonstrating: (1) non-linear enhancement of crystallinity with a 93.7% increase in crystallite size (25.15 nm undoped to 48.72 nm at 3 at.% Al) and 73.4% reduction in dislocation density (1.581 x 10(15) to 0.421 x 10(15) lines/m(2)); (2) emergence of unique acicular morphology with 22% greater surface area at 3 at.% Al; (3) precise ar tuning from 3.131 eV to 2.796 eV while maintaining high transmittance; and (4) comprehensive characterization including Raman spectroscopy showing E-2(high) mode shifts from 437 cm(-)(1) to 433 cm(-)(1) with doping, XPS confirming Al-3(+) incorporation at 73.8 eV binding energy, and BET analysis revealing increased surface area from 320 m(2)/g to 380 m(2)/g with enhanced mesoporous (65% of total volume) and microporous (15% increase) characteristics. The work reveals three key innovations: (1) identification of optimal 2 at.% Al doping concentration that maximizes both crystallinity (32.92 nm crystallites) and optical performance (2.94 eV bandgap); (2) discovery of competing size-strain effects enabling simultaneous property enhancement; and (3) development of reproducible bandgap engineering process. The specific objectives were to synthesize pure and Al-doped ZnO films (0, 2, and 3 at.%) using RF magnetron sputtering and characterize them using X-ray diffraction (XRD), surface morphology analysis with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-visible spectroscopy, Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Surface Area and Porosity Analysis. XRD analysis revealed all films exhibited polycrystalline wurtzite structure with preferential c-axis orientation. SEM demonstrated a morphological transition from hexagonal grains (undoped) to acicular structures (3 at.% Al). Optical characterization confirmed high transmittance (> 85%) and bandgap reduction from 3.131 eV (undoped) to 2.796 eV (3 at.% Al). These results demonstrate that 2 at.% Al-doped films achieve optimal balance between structural perfection (32.92 nm crystallites, 0.922 x 10(15) lines/m(2) dislocation density) and optical functionality (2.94 eV band gap, > 85% transmittance), making them ideal for transparent conductive oxides in LEDs and solar cells. The quantitative correlations established enable precise engineering of doped ZnO systems for optoelectronic applications.