The Influence of Film Thickness on the Transparency and Conductivity of Al-Doped ZnO Thin Films Fabricated by Ion-Beam Sputtering

Abstract

To evaluate the influence of film thickness on the structural, electrical, and optical properties of Al-doped ZnO (AZO) films, a set of polycrystalline AZO samples with different thickness were deposited on glass substrates by ionbeam sputtering deposition (IBSD). X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS), four-point probe measurements, and spectrophotometry were used to characterize the films. XRD showed that all the AZO films had preferred c-axis orientation. The ZnO (110) peak appeared, and the intensity increased, with increasing thickness. All the samples exhibited compressive intrinsic stresses. AFM showed that the grain size along with the root-mean-square (RMS) roughness increased with increasing thickness. The decrease of resistivity is due to the corresponding change in grain size, surface morphology, and chemical composition. The average optical transmittance of the AZO films was over 80%, and a sharp fundamental absorption edge with red-shifting was observed in the visible region. The optical band gap decreased from 3.95 eV to 3.80 eV when the AZO film thickness increased from 100 nm to 500 nm.

Elaboration of high-transparency ZnO thin films by ultrasonic spray pyrolysis with fast growth rate

“…Similar temperature effects were reported in the AFM study by Prasada Rao et al [21]. The RMS roughness obtained for the ZnO thin films deposited with ultrasonic spray pyrolysis at 450 • C from a pH 4 solution compares well with values usually measured for ZnO films obtained by more complex techniques such as ion-beam or RF magnetron sputtering [52,53].…”

Improving the uncommon (110) growing orientation of Al-doped ZnO thin films through sequential pulsed laser deposition

“…This growing mode was not observed so far for AZO films obtained particularly by SPLD method and, generally, by any other method on amorphous substrate. In return, a similar behavior has been noted previously for AZO films deposited by ion sputtering [36] and by magnetron sputtering techniques [12]. The growth of the film in the (110) plane direction was attributed to an increase of the film thickness (noted by d in Table 2), which would promote crystallite growth along directions other than along the ZnO c-axis.…”

“…The position of the (002) peak shifts toward lower 2θ angles with Al percentage, which is equivalent to an increase of the lattice constant c. Since the radius of Zn 2+ is larger than the substituting Al 3+ , a decrease of lattice parameters is expected comparing with undoped ZnO. The increase of the lattice parameter which occurs in our case may be explained by that the aluminum ions are present in interstitial positions in the host lattice [1,36,37]. We believe that this type of doping is due to the fact that the energetic species, which are a signature for the ablation plasma [22], can penetrate the previously deposited layer and end up in non-lattice node positions, especially when no supplementary heating of the substrate is performed.…”

Improved structural and electrical properties of thin ZnO:Al films by dc filtered cathodic arc deposition

“…It is known that the electrical and optical properties of transparent conducting oxide (TCO) thin films, including ITO, [1][2][3] fluorine doped tin oxide (FTO), [4][5][6] gallium doped zinc oxide (GZO) 7,8 and AZO [9][10][11] are strongly dependent on film thickness. ITO is often preferred for its excellent properties but its cost is high due to increasing demand for displays, solar cells, and smart windows.…”