Dielectric function of sol-gel prepared nano-granular zinc oxide by spectroscopic ellipsometry

Abstract

ZnO thin films have been prepared by sol gel and deposited by spin coating. The dielectric function has been determined by spectroscopic ellipsometry. Ellipsometric spectra are inverted by a direct numerical method without using the standard fitting procedures. The obtained dielectric function presents a broad excitonic effect. The dielectric function is studied using Elliot excitonic theory including exciton plus band-to-band Coulomb interactions with standard Lorentzian broadening. A modification of this model dielectric function with independent bound and unbound exciton contributions is empirically proposed to improve modelling of the band gap excitonic peak.

Comparative study of ZnO optical dispersion laws

“…  values are large than 1 as it is well known for semiconductor material. Generally the value of   reported in literature is ranging from 1.54 to 2.66 [19,[38][39][40]. This is the case for the Tanguy dispersion law comparing to higher values obtained by FB and TL.…”

“…Therefore, it has become essential to control the optical constants of ZnO. Spectroscopic ellipsometry technique is a relevant tool for such optical analysis [8][9][10][11][12][13][14][15][16][17][18][19]. In the previous works in literature, dispersion laws such as Cauchy [8,9], Forouhi-Bloomer [8,9], Tauc-Lorentz [9][10][11][12], Tanguy [13,14] or wavelength-by-wavelength method [20,21] were used to extract the optical constants of ZnO by modeling spectroscopic ellipsometry (SE) data.…”

Correlated effects of preparation parameters and thickness on morphology and optical properties of ZnO very thin films

“…Excitons indeed generate optical absorption of photons with energy slightly below the band gap to create an interacting electron-hole pair. A physical description of the dielectric function of the sol-gel ZnO has been the subject of an other work [34], so that we will only focus on the evolution of the dielectric function with thickness and preparation parameters. Beyond the characteristic features of the dielectric function, a striking increase of both real and imaginary parts of the dielectric functions is observed over the whole spectrum for the different synthesis temperature and sol concentration sets when the number of deposition cycles is increased.…”

“…In other works we have reported a detailed investigation of the dielectric function of sol-gel derived ZnO [34] and evidenced the effects of thickness on optical properties and morphology simultaneously [35]. A sol-gel recipe is used to obtain very thin layers of granular ZnO with thickness from 15 to 150 nm.…”

Effects of Ag Nanoparticles on Zinc Oxide Photocatalytic Performance

“…ZnO/Ag NPs nanocomposite thin films were deposited by a one-step sol-gel spin coating technique [41]. The ZnO precursor solution was obtained by dissolving zinc acetate dihydrate (Zn(CH 3 CO 2 ) 2 •2H 2 O) in 1-propanol (C 3 H 8 O).…”