High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation

Abstract

Five hundred-nanometer-thick ZnO-based textured polycrystalline films consisting of 490-nm-thick Al-doped ZnO (AZO) films deposited on 10-nm-thick Ga-doped ZnO (GZO) films exhibited a high Hall mobility (μ H) of 50.1 cm 2 /Vs with a carrier concentration (N) of 2.55 × 10 20 cm −3. Firstly, the GZO films were prepared on glass substrates by ion plating with dc arc discharge, and the AZO films were then deposited on the GZO films by direct current magnetron sputtering (DC-MS). The GZO interface layers with a preferential c-axis orientation play a critical role in producing AZO films with texture development of a well-defined (0001) orientation, whereas 500-nm-thick AZO films deposited by only DC-MS showed a mixture of the c-plane and the other plane orientation, to exhibit a μ H of 38.7 cm 2 /Vs with an N of 2.22 × 10 20 cm −3 .

Comparing Thermal Durability and Effects of Annealing Temperature on Characteristics of Hydrogen-Doped ZnO, AZO, and GZO Thin Films

“…In Figure 1(a), for as-deposited films, n values of AZO-H and GZO-H films are higher than those of ZnO-H film, which indicates that group III elements effectively substituted for Zn atoms in ZnO lattice. The μ values for all films without undergoing annealing process are quite high in comparison with published reports for the similar materials and technique [21,22]. Besides, in Figure 1(b), hydrogen shows the ability to improve the electron mobility for unannealed AZO-H and ZnO-H films better than unannealed GZO-H films.…”

Improvement of the Properties of Direct-Current Magnetron-Sputtered Al-Doped ZnO Polycrystalline Films Containing Retained Ar Atoms Using 10-nm-Thick Buffer Layers

“…20 On the other hand, the peaks originating from the (112̅ 2) and (112̅ 4) orientations disappeared together with that originating from the (101̅ 1) orientation for the buffer-layer-free AZO film at a substrate position of 6.5 cm, as shown in Figure 2b. 30,[32][33][34]40 To estimate the texture evolution quantitatively, we examined the variation of the volume fraction of (0001) orientation (V (0001) ) obtained from the XRD pole figure measurements. Figure 3a−c shows XRD pole figures of the 0002 reflections of the same films in Figure 2, respectively.…”

“…The reflections observed in the out-of-plane GI-XRD measurements and their origins were as follows: (I) solid black inverted triangles (▼) indicate the 0002 reflections, which correspond to components originating from the (0001) orientation owing to the tilting of columnar grains with the (0001) orientation; (II) solid black circles (•) indicate the other reflections besides the 0002 and 101̅ 3 reflections, which correspond to components originating from other orientations; and (III) solid black diamonds (⧫) indicate the 101̅ 3 reflections, which correspond to the trajectory of the scattering vector when the films possess a (0001) orientation and/or other orientations. [32][33][34]39,40 The out-of-plane GI-XRD patterns of all of the buffer-layerfree AZO films in Figure 4a show 0002 and 101̅ 3 reflections. For the 15-nm-thick AZO film at a substrate position of 0.5 cm, as shown in the upper part of Figure 4a, 0002 and 101̅ 3 reflections were observed.…”

“…The ellipsometric data (Ψ and Δ) were acquired in the wavelength ranges of 0.3−1.7 μm (M-2000DI) and 1.7−30 μm (IR-VASE Mark II) at incident angles of 55, 65, and 75°. For a comprehensive analysis of the texture, we conducted out-of-plane grazing-incidence (GI) X-ray diffraction (XRD) measurements [32][33][34]39,40 using a SmartLab XRD system (Rigaku Corp.) with Cu Kα ̅ radiation (wavelength λ = 0.15418 nm, based on the weighted average of Cu Kα 1 (λ = 0.154059 nm) and Cu Kα 2 (λ = 0.15444 nm) in an intensity ratio of 2:1), where the substrate surface was subjected to Xray irradiation at an incident angle (ω) of 0.35°and only the 2θ axis was scanned. The textures of the bulk AZO films were characterized on the basis of out-of-plane wide-range reciprocal space maps (RSMs) 20,[32][33][34]37 and pole figures 30,33,34,39 by a SmartLab XRD system equipped with a PILATUS 100K/R two-dimensional X-ray detector using Cu Kα ̅ radiation.…”

UV-irradiated sol-gel spin coated AZO thin films: enhanced optoelectronic properties

“…AZO thin films have a persistent photoconductivity because of activation due to light irradiation. UV irradiation for a long period affects excitation and activation of conduction band electrons and thus upgrades the electrical conductivity [46].…”