Investigation of textured Al-doped ZnO thin films using chemical wet-etching methods

In this study, the optical properties and morphologies of Al-doped ZnO (AZO) films textured by the chemical wet-etching method with three different acid species are investigated. An initial AZO film is sputtered on a glass substrate by rf magnetron sputtering. The film surface was then textured by wet-etching using diluted HCl, HNO₃ or H₃PO₄. The average transmittance of all the post-treated ZnO:Al films remains around 75-80% as measured by a UV-vis analyzer. A haze ratio calculation shows that the light scattering properties can be significantly controlled by varying the etchant species, acid concentration, and etching time. Atomic force microscopy (AFM) was used to find the average roughness of the textured AZO films. In this study, the HNO₃ etchant gives the highest haze ratio of 49.2% at a wavelength of 550 nm. The textured ZnO:Al films with an electrical resistivity of 5.47 × 10^-4 Ω-cm, carrier concentrations of 3.98 × 10²⁰ cm^-3 and mobility of 28.7 cm² V^-1 s^-1, can be obtained when etched in diluted HNO ₃ for 60 s. It is found that the chemical wet-etched AZO glass substrate appears to be helpful in enhancing the short circuit current (J _sc) when applied on silicon thin film solar cells.