Optical Properties of Annealed ZnO Thin Films Fabricated by Pulsed Laser Deposition

Abstract

The annealing effects on the structural and optical properties of grown ZnO thin films fabricated by pulsed laser deposition were investigated by using different techniques. The XRD reveals the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The average grain size (D) of annealed ZnO nanocrystalline thin films is found to be in the range 7.77-15.91 nm. SEM of the thin film consisted of many grains distributed uniformly throughout the surface. TEM shows a relatively smooth surface with an average nanocrystalline size of 13 nm in close agreement with the XRD result. The transmittance spectra demonstrate the highly transparent nature of the films in the visible region (>70 %). The calculation of optical band gap energy (E g ) is found to be in the range 2.95-3.23 eV. The PL spectra show that the amorphous film gives a UV emission only and the annealed nanocrystalline films produce UV, violet, blue and green emissions which indicate that the point defects increased as the amorphous film was annealed. It is concluded that the structural, optical and emission properties of ZnO films grown on glass substrates by PLD strongly depend on the annealing times. The results demonstrate that these annealed films are promising materials for optical component applications.

Influence of the Zn plasma kinetics on the structural and optical properties of ZnO thin films grown by PLD

“…The E g values shown in Table 1 are similar to those reported in literature [5][6][7]. Note that the highest E g value corresponds to the film grown at 40 eV, which according to XRD results has a higher crystalline quality, this band gap value is near to the reported value of high-quality ZnO [3,4].…”

“…In particular, zinc oxide (ZnO) is a promising semiconductor for optoelectronic applications because it has a direct band gap (E g ) of 3.37 eV at room temperature (RT), it is transparent in the visible range (400-700 nm), and it has an excitonic binding energy of 60 meV [3,4]. It can offer light emissions in the visible range, which are attributed to intrinsic defects such as zinc interstitials (Zn i ), zinc vacancies (V Zn ), oxygen vacancies (V O ), oxygen interstitials (O i ) and oxygen antisites (O Zn ) [5][6][7]. Additionally, ZnO presents nonlinear optical properties that can be used in applications such as frequency converters and logic elements in the nanoscale optoelectronic circuitry [8,9].…”

“…When grown as a thin film [5], in which thickness variation (size effect), substrate type and annealing have an effect on the optical properties [10], it can be used to fabricate UV light-emitting diodes and transparent thin-film transistors. The properties of ZnO thin films have been widely studied for a large variety of deposition methods and experimental conditions.…”

“…These energy conditions, along with directionality in the plasma, give to PLD advantages for deposition using background reactive gasses, since the reactions required to achieve the desired oxide stoichiometry are more effective [17]. The physical properties of ZnO thin films grown by PLD have been widely studied, regarding the influence of substrate [18][19][20][21] and annealing temperature [5,6,22], oxygen pressure [6,7,15,23], substrate type (quartz [24], silicon [25], diamond-like carbon [26], sapphire [9] or glass [27]) and targets [28]. Furthermore, experimental parameters, as well as the deposition techniques, have been optimized to achieve materials with high crystalline quality [29,30].…”

Self-Confined Precipitation of Ultrasmall Plasmonic Cu2–xSe Particles in Transparent Solid Medium

“…As shown in Figure b,c, the plasmonic resonance peak shifts from 1400 to 1140 nm as the Se/Cu ratio increased from 5 to 40 as a result of increase in hole concentration. We then employ the Drude model , and Tauc’s law , to calculate the free carrier (holes) density ( N h ) and the optical band gap ( E g ) of the Cu 2– x Se NP-doped glass with different Se/Cu values (i.e., different copper deficiencies), respectively (see Supporting Information). As shown in Figures c and S3c,d, the calculated free carrier density (17.16 → 14.07 × 10 21 cm –3 ) and direct (2.93 → 2.52 eV) and indirect band gaps (2.01 → 1.63 eV) (Figure d) decrease with the increase of the Se/Cu ratio.…”