Optical and electronic properties of post-annealed ZnO:Al thin films

Abstract

This study examined the optical and electronic properties of post-annealed Al-doped ZnO ͑ZnO:Al͒ thin films. The lowest resistivity was observed after annealing a sputter-deposited ZnO:Al film at 350°C. X-ray photoelectron spectroscopy revealed a ϳ0.4 eV shift in the Fermi level when the carrier concentration was increased to 1.6ϫ 10 20 cm −3 by Al doping and annealing. The optical band gap increased from 3.2 eV for insulating ZnO to 3.4 eV for conducting ZnO:Al, and was associated with conduction-band filling up to ϳ0.4 eV in a renormalized band gap. Schematic band diagrams are shown for the ZnO and ZnO:Al films.

The influence of Ce doping on the structural and optoelectronic properties of RF-sputtered ZnO films

“…Optical absorption studies show that the absorption edge of the doped films shifts towards blue region with a widening of the band gap at a higher energy. Such a feature is related to the rising Fermi level by filling more electrons in the conduction band (Burstein-Moss effect) (Dondapati et al 2013;Kim et al 2010b;Luo et al 2012). When Ce atoms are incorporated into ZnO, both ions ðCe 3þ ; Ce 4þ Þ, whether in substitutional or interstitial sites, tend to increase the carrier concentration.…”

“…Several techniques have been used to grow ZnO films, such as pulsed laser deposition (Sachet et al 2013), DC reactive-magnetron sputtering (Suchea et al 2006;Logothetidis et al 2008), atomic layer deposition (Frölich and Wegener 2011), ZnO films deposited by RF magnetron sputtering depend on the deposition parameters involved in the growth process, such as the RF power, sputtering gas pressure, gas flow rate, and temperature. By adjusting these processing parameters, ZnO films with properties that are compatible with optical devices may be obtained (Al-Kuhaili et al 2012;Lin et al 2004;Kim et al 2010b;Kapustianyk et al 2007). Additionally, doping with selective elements can induce changes in the structural, electrical, optical, and electronic properties of ZnO films (Morinaga et al 1997;Kim et al 2010a;Joshi et al 2010).…”

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

“…Aluminum is a well known dopant for increasing the electron carrier concentration of ZnO for TCO applications. 18,19 In this study, we report that the electron carrier concentration of ALD Zn(O,S) can be either increased or decreased by modifying the stoichiometry of the film with aluminum incorporation, which is potentially useful for graded buffer layers in thin-film solar cell applications.A custom-built hot-wall ALD reactor was used to grow Zn(O,S) and Al-incorporated Zn(O,S) films. Films were grown at a deposition temperature of 120°C in closed valve mode.…”

Influences of defects evolvement on the properties of sputtering deposited ZnO:Al films upon hydrogen annealing

“…Optical band gap can be extracted from the measured T and R spectra by the Tauc's relation. 37 Figure 6(c) shows that the optical band gap increases monotonously from 3.49 to 3.83 eV with the increase of annealing temperature up to 550 o C, and then decreases to 3.77 eV when the annealing temperature further increases to 625 o C. Due to the Moss-Burstein effect, 38 the changing trend in optical band gap is a direct indication of the variation in the carrier concentration, which will be discussed in the following section. ∼0.7 wt.% at 500 o C in the first heating run, while it is negligible in the second and third thermal cycles, thus the mass loss cannot be attributed to the hydrogen etching effect.…”