Effects of aluminum doping on the structural and optical properties of ZnO nanorods grown on highly conductive films

ZnO nanorods were grown on ∼ 50-nm-thick transparent conductive oxide thin films by hydrothermal synthesis. The resistivity of the ZnO films was lowered to 4 × 10⁻⁴ Ω cm upon Ga doping. Zinc nitrate hexahydrate, mixed with hexamethylenetetramine, was dissolved in deionized water to prepare a synthesis solution. Aluminum nitrate nonahydrate was added to the synthesis solution to dope the Al into ZnO nanorods. X-ray diffraction analysis and field-emission scanning electron microscopy were conducted to study the crystal structure and morphology of the nanorods, respectively. Al doping enhanced the preferential orientation to (002) of a wurtzite structure and increased the compressive strain. The trace of Al in the ZnO nanorods was detected by energy dispersive X-ray spectroscopy. The optical properties were investigated by measuring the transmittance, Raman shift, and photoluminescence. Al doping led to a blue shift or red shift in the energy band gap. The results of the Raman shift confirmed the compressive stress in the ZnO nanorods. Sharp ultraviolet (UV) and broad visible photoluminescence peaks were obtained irrespective of Al concentration in the ZnO nanorods. The intensity of the UV peak doubled by Al doping.