Enhanced Piezoelectric Performance in ZnO Thin Films by Gallium and Aluminum Doping for Energy Harvesting Applications

This study investigates the enhancement of piezoelectric properties in zinc oxide (ZnO)-based thin films through gallium (Ga) and aluminum (Al) ion doping, using sol-gel and hydrothermal methods. ZnO is widely used due to its excellent piezoelectricity, chemical stability, and abundance. Ga and Al ions, with radii similar to Zn²⁺, were doped into ZnO films to improve carrier concentration, resistivity, and piezoelectric output. Three doping processes and two concentrations (1% and 3%) were explored, with results showing reduced resistivity, widened band gaps, and increased transmittance for both gallium-doped (GZO) and aluminum-doped (AZO) films compared to pure ZnO. GZO films exhibited superior performance, with the lowest resistivity (0.0065 Ω·cm) and the highest piezoelectric output at 20 Hz. However, excessive doping (3%) increased lattice defects, reducing output power due to stress and electron migration effects. Durability tests confirmed excellent mechanical stability of both GZO and AZO devices under extended vibration, with GZO showing the most stable output power. These findings suggest that Ga and Al doping can significantly enhance the piezoelectric efficiency of ZnO thin films for energy harvesting applications.