Elucidating the microstructural and optoelectronic properties evolution of sputtered Al-doped MZO thin films

This study involves the deposition of magnesium-doped zinc oxide (MZO) thin films through radio frequency (RF) magnetron sputtering, followed by annealing at temperatures of 350 degrees C, 450 degrees C, and 550 degrees C. Since there is no significant impact of annealing temperatures on MZO thin films, MZO and aluminium-doped zinc oxide (AZO) were co-sputtered to deposit Al-doped MZO (AMZO) thin films. The grown AMZO films were subsequently annealed at 350 degrees C, 450 degrees C and 550 degrees C to regulate their microstructural and optoelectronic characteristics. The Xray diffraction (XRD) analysis revealed that AMZO films exhibited a predominant (0 0 2) orientation with a single intense diffraction peak, showcasing a wurtzite structure. The field emission scanning electron microscopy (FESEM) presented an increment in grain size for MZO and AMZO films from 31.3 to 64.7 nm and 57.0-64.8 nm, respectively. Furthermore, the atomic force microscopy (AFM) analysis demonstrated a substantial reduction in surface roughness from 1.67 to 1.58 nm for AMZO films annealed at 550 degrees C compared to MZO films. Notably, the optical band gap changed from 3.64 to 3.32 eV, which was influenced by both the Al content and annealing temperature. The carrier concentration for as deposited and annealed MZO films remained in the orders of 1014 cm-3, whereas AMZO and AMZO films annealed at 550 degrees C exhibited higher carrier concentrations, in the orders of 1016 cm-3 and 1020 cm-3, respectively. Remarkably, low resistivity (2.10 x 10-2 Omega cm) was observed for AMZO films annealed at 550 degrees C. Based on these findings, AMZO films exhibited prospect as a buffer layer for CdTe thin films solar cell applications.