Tailoring the Structural and Optoelectronic Properties of Al-Doped Nanocrystalline ZnO Thin Films

Abstract

This paper describes the effect of Al doping (0 at.% to 6 at.%) on the structural and optoelectronic properties of nanocrystalline ZnO thin films deposited by thermal evaporation. X-ray diffraction patterns confirm that an increase in Al concentration (from 0% to 6%) in ZnO lowers the crystallinity of the films and reduces grain size. Al doping is also found to influence the optical properties of the ZnO thin films. Visible transmittance above 85% was obtained by increasing the Al doping to 6%. The optical bandgap was found to vary from 3.20 eV to 3.97 eV with changing Al content from 0% to 6%, which is in accordance with the Burstein–Moss shift. The mobility of ZnO thin films can be varied from 5.60 cm2/Vs to 24.25 cm2/Vs, the carrier concentration from 5.93 × 1018/cm3 to 9.11 × 1020/cm3, and the resistivity from 4.62 × 10−4 Ω cm to 4.34 × 10−2 Ω cm, depending on the Al doping concentration (0% to 6%). This study suggests that ZnO:Al films can be tailor-made to meet the requirements for various optoelectronic applications such as flexible photocells or ultraviolet (UV) photodetectors covering a wide range of short wavelengths.