An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique

Abstract

Zn₍₁₋ₓ₎MgₓO thin films with various concentrations of magnesium were deposited using the spray pyrolysis method. The transmittance spectra recorded for all films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite structure increases from 3.22 to 3.60 eV by incorporating Mg into ZnO. However, when the atomic ratio of Mg exceeded 0.4, a second crystalline phase (assigned to cubic MgO) became discernible in XRD patterns, a compressive strain was observed in the wurtzite lattice, and crystallite sizes decreased significantly. In accordance with these observations, finer grains with a pronounced columnar growth were observed in 3D AFM representations, and the surface roughness decreases significantly. Finally, selective etching in water yields porous films with a great surface-to-volume ratio, a lower refractive index, and a better light transmission. These porous films with tunable band gaps seem to be excellent candidates for various interesting applications.