The Role of Al Doping on ZnO Nanowire Evolution and Optical Band Gap Tuning

In this work, the morphological transformation and band gap modulation of ZnO by Aluminum doping has been investigated. Pure ZnO and Aluminum doped Zinc oxide (Al:ZnO) nanostructure have been fabricated using hydrothermal method on the seed layer coated FTO substrates. The prepared samples were investigated with such analytical techniques as Raman spectroscopy, Field Emission scanning electron microscope (FESEM), Photoluminescence (PL) and spectrophotometer. Raman spectra revealed E-2 (high) and E-1 (low) vibrational modes for pure ZnO. However, a successive shift in E-2 (high) mode towards higher wavenumbers has been observed by placing ZnO with different concentration of Aluminum nitrate nano-hydrate solution (0.1 mM, 0.2 mM and 0.3 mM) confirming the sequential Al incorporation in the ZnO nanostructure. SEM results show the morphological transformation from a typical hexagonal ZnO nano-wire to petal shaped nano-rods with the increase of Al concentration. The optical properties have been investigated using the photoluminescence (PL) and optical transmission. In the PL spectra, pure ZnO nanostructure has UV peak with higher intensity compared to the visible peak. However, the addition of Al in the ZnO causes enhanced emission in the visible region compared to the UV emission. The addition of Al in ZnO nanostructure also modifies the optical band gap of ZnO from 3.2 to 3.15 eV.