Tuning ZnO thin films via aluminum doping synthesized by co-sputtering: structure, optics, and photoconductivity

Aluminum-doped zinc oxide (AZO) thin films are promising for optoelectronic applications, such as transparent electrodes and photodetectors, due to their excellent optical and electrical properties. In this study, AZO thin films were synthesized on glass substrates via co-sputtering using separate ZnO and Al targets. By varying the DC power applied to the Al target (10–25 W), the aluminum doping concentration was controlled, producing samples labeled AZO-10, AZO-15, AZO-20, and AZO-25. The structural, optical, electrical, and photoconductive properties were characterized using XRD, EDX, UV–vis spectroscopy, Hall effect measurements, and I–T (current–time) analysis. XRD revealed an amorphous structure due to low deposition temperatures. EDX confirmed an increase in aluminum content from 0.30% to 1.82% with higher sputtering power. Optical properties exhibited reduced transmittance and a widened bandgap (3.38 eV –3.55 eV), attributed to the Burstein-Moss effect and lattice strain. Electrical properties showed enhanced conductivity, with sheet resistance decreasing from 1.43 × 10 6 to 1.21 × 10 4 Ω/□ and carrier concentration increasing from 1.30 × 10 13 to 5.35 × 10 14 cm −2 , though carrier mobility was limited by the amorphous structure. Photoconductivity measurements under periodic LED illumination demonstrated stable, repeatable photoresponse, with photocurrent decreasing from 120 mA in AZO-10 to 20 mA and 8 mA in AZO-20 and AZO-25, respectively, due to defect states acting as traps and recombination centers induced by higher doping. This study highlights the critical role of optimizing aluminum doping to balance optical transparency, electrical conductivity, and photoconductive performance, establishing co-sputtering as an effective method for tailoring AZO thin films for optoelectronic applications