Precise determination of optical band gap in Cr-doped semiconductor nanowires

• Published in: Optical and quantum electronics Vol. 54; no. 2
• Main Authors: Anad, Noori S., El-Fattah, Zakaria M. Abd, Attallah, M., Ahmed, Hanaa M., El-Okr, M. M., El-Bahnasawy, H. H.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2022; Springer Nature B.V
• Subjects: Absorption; Characterization and Evaluation of Materials; Computer Communication Networks; Crystal structure; Doping; Electrical Engineering; Energy gap; Lasers; Nanoparticles; Nanowires; Optical Devices; Optical resonance; Optics; Photoluminescence; Photonics; Physics; Physics and Astronomy; Trivalent chromium; Wurtzite; Zinc oxide; Optical absorption spectroscopy; Semiconductor nanoparticles; Transition metals; Diluted magnetic semiconductors; Optical band gap; Elemental analysis
• ISSN: 0306-8919; 1572-817X
• DOI: 10.1007/s11082-021-03462-1

Pristine and chromium-doped ZnO nanowires were prepared following the traditional co-precipitation method. X-ray diffraction data identified a pure wurtzite hexagonal crystal structure characteristic for ZnO, irrespective of the doping level. The particle size, as deduced form Williamson–Hall plots, was found to be 45–55 nm for all samples. Scanning electron microscopy revealed a clear nanowires morphology for the pure and doped samples, while elemental analysis ensured the successful Cr-doping. Distinct spectroscopic signatures of Cr-doping were revealed from a detailed deconvolution process applied to optical spectra of doped samples, where Cr 3+ optical transitions were unambiguously identified at ~ 420 and ~ 665 nm. Particularly relevant, is the spectral decomposition here performed for the superimposed absorption edge (~ 385 nm) and Cr 3+   optical resonance at ~ 420 nm, allowing to claim practically doping-independent optical band gap behavior in the present doping regime. This is further supported by identifying the characteristic ZnO near edge photoluminescence peak (~ 392 nm) which maintains fixed wavelength after Cr-doping. These findings contrast earlier studies on Cr-doped semiconductor nanoparticles and glass systems where the optical band gap has been largely underestimated. We attribute the inconsistence band gap values reported in literature for Cr-doped semiconductors to the proximity of Cr optical transitions to the semiconductor absorption edge. Graphical abstract