Optical properties of Al-doped ZnO thin films obtained by the method of high-frequency magnetron sputtering

Abstract

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index [Formula: see text], absorption coefficient [Formula: see text], extinction coefficient [Formula: see text], dielectric functions [Formula: see text] and optical conductivity [Formula: see text]) of thin films and thickness [Formula: see text] can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Effect of Al doping on optical properties of ZnO thin films: theory and experiment

“…The obtained value of the ZnO: Al thin film thickness is 454.83 nm. The optical properties of a thin film (refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ), dielectric functions ε(λ), optical conductivity σ(λ) and thickness d) can be easily evaluated from a transmission spectrum with interference effects using the envelope method [26][27][28][29][30][31] (Fig. 2).…”

Optical and Dispersion Parameters of the Al-doped ZnO Thin Film

“…Al-doped ZnO (ZnO:Al) thin films were deposited on glass substrates with a size of 16  8  1.1 mm 3 by the method of high-frequency (HF) magnetron sputtering (~ 13.6 МHz) using a VUP-5M vacuum station (Selmi, Ukraine) [9,27]. As a target the disc from sintered ZnO (purity of 99.99 %) powder with Al2O3 (2.5 wt.%) admixture was used.…”

“…Spectral dependences of the optical transmittance (Shimadzu UV-3600) of the title samples have been measured in the visible and near infrared regions (300-2500 nm) at room temperature [9,27].…”

“…The optical band gap Eg is also determined from the spectrum of the absorption coefficient (hν). For this purpose, the known Tauc relation for the direct optical transition between the valence and conduction bands is used [9,27],…”

“…It is known that optical properties of semiconductor thin films depend on the deposition method [9,10]. Currently, various methods are used to obtain ZnO thin films: radio frequency (RF) or direct current sputtering, spray pyrolysis, spin coating, metal organic chemical vapor deposition and pulsed laser deposition [5][6][7][9][10][11][12][13][14][15][16][17][18][19].…”