Characterization of sol gel Zn1-xCaxO thin layers deposited on p-Si substrate by spin-coating method

Abstract

Thin films Zn1-xCaxO (0≤x≤6%) on a p-Si substrate are elaborated by sol-gel process and spin coating. X-ray diffraction displays a hexagonal wurtzite structure with an increase of lattice parameters confirming the substitution of Zn 2+ by Ca 2+ . The estimation of crystallite sizes along the three main crystallographic planes is practically constant (22 nm) suggesting a spherical symmetry shape of the crystallites which is confirmed by SEM. UV-visible reflectance spectra attest a band gap tuning from 3.144 to 3.262 eV which is confirmed by the PL measurement at 2 K for Zn0.94Ca0.06O sample by the appearance of a broad band around 3.508 eV. Although the luminescence of the samples is weak, we well distinguish the free exciton emission (FXA ) positioned at 3.376 eV and the bound exciton recombination (D 0 X) around 3.362 eV.

Microstructural, optical, and electrical properties of Eu, Tb co-doped ZnO micropods elaborated by chemical bath deposition on a p-Si substrate

“…Williamson and Hall (WH) method was used to distinguish the part contribution of crystallite size (t WH ) and strain () in the full width at half maximum (FWHM) of X ray diffraction peak as described in reference [35]. WH crystallite sizes, strain and dislocation density as function of Eu and Tb concentration obtained from EDX measurements are also regrouped in Table 6.…”

Characterization of Eu doped ZnO micropods prepared by chemical bath deposition on p-Si substrate

“…The p (hkl) of commercial ZnO powder (Sigma-Aldrich inventory: 1314-13-2), calculated from the XRD spectrum measured under the same conditions, is also shown for comparison. The values of the orientation parameter obtained for our micropods show a preferential orientation along the axis [100], which is different from that of the powder ([101]), thin film [40,41], and nanorods ([002]) [42]. As the micropods grow along the c-axis of the wurtzite structure, perpendicular to the [100] direction, most of the deposited ZnO micropods are longitudinally on the surface of the silicon substrate (micropods tend to orient flat on a substrate upon drying) and the other is randomly oriented, which explains the low intensity of other X-ray peaks.…”

“…This arrangement of micropods can be explained by the small lattice mismatch between the substrate (a = 5.43 Å) and ZnO (c = 5.20 Å). The lattice parameters "a" and "c" for doped ZnO micropods deposited on p-Si substrates are calculated and listed in Table 3 by using the following equation [41]:…”

“…Because the radial direction [110] is orthogonal to the c-axis, the diameter of this crystallite can be assimilated to the crystallite size estimated using the FWHM of the (110) planes. The dislocation (line defects in the regular crystal lattice) density (δ) along the crystallographic plane (hkl) can be calculated using the formula [41]:…”

“…Our samples are thick (thickness ≥1 μm), which prevents accidental loss by partial transmission when measuring the percent reflectance. The detailed optical band gap determination of our samples is described in our recent paper [41]. The corresponding values are listed in Table 7 as function of the X Eu concentration.…”