Structural, morphological and optical properties of ZnO nanorods grown on a ZnO:Ga seeded thin film: The role of chemical bath deposition precursor concentration at constant and varying II/VI molar ratios

• Published in: Thin solid films Vol. 687; p. 137483
• Main Authors: Ungula, J., Swart, H.C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2019
• Subjects: Dye sensitize solar cells; Nanorods; Precursor concentrations; Semiconductors, gallium-doped zinc oxide; Dye sensitize solar cells; Semiconductors, gallium-doped zinc oxide; Nanorods; Precursor concentrations
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2019.137483

ZnO nanorods (ZNRs) were synthesized on glass substrates coated with an optimized Ga-doped ZnO seed layer by a two-step chemical bath deposition technique at constant and varying Zn(NO3)2/C6H12N4 (II/VI) molar ratios of the precursor solutions for growth time of 90 and 180 min and growth temperature of 90° C. The effects of different equimolar precursor solution concentrations (Cs) ranging from 0.01–0.2 M, as well as the varying II/VI molar ratios (ranging from 1:0.1–1:2) of the growth solutions were investigated on the morphology, luminescence and optical properties of the ZNRs. The X-ray diffraction analysis revealed that the as-grown ZNRs have a crystalline hexagonal wurtzite structure and they were preferentially oriented along the c-axis in all cases. The crystallite size of the ZNRs and the relative intensity of the (002) peak were observed to increase with the increase in Cs and II/VI molar ratios of the precursor solution. An appreciable peak shift of the (002) plane of the ZNRs, to lower 2θ angle with increasing molar ratios of the Cs was observed. The scanning electron microscope images illustrated that the ZNRs morphologies improved, their lengths and diameters increased as the growth Cs and II/VI molar ratios were raised. The root means square surface roughnesses of the ZNRs were found to reduce from 70 to 22 as the II/VI molar ratios increased from 1:0.1 to 1:2. The photoluminescence (PL) spectra displayed the prominent Ultra violet (UV) and deep level emissions (DLE) in both instances. The exciton peak intensity increased to a maximum value up to 0.05 M Cs and the II/VI precursor ratio of unity and decreased when the Cs levels and molar ratios were increased further. The calculated PL emission intensity ratio (IUV/IDLE) was found to be 12.5, 1.9 and 0.8 for 0.01, 0.05 and 0.1 M, respectively, which suggests that the ZNRs grown with the higher equimolar Cs possessed a high optical quality. The UV–Vis analysis also showed greatly enhanced optical absorbance in the visible region at higher Cs and II/VI molar ratios. Similarly, the band gap energy decreased from 3.28–3.25 eV and from 3.30–3.24 eV with the increase in the Cs and II/VI molar ratios, respectively. •Crystallinity of ZnO nanorods improved with an increase in precursor concentration.•Improved uniformity and alignment with an increased diameter and length obtained.•Enhanced optical absorbance at higher precursor concentration.•Photoluminescence intensity increased at higher precursor concentration.