Preferential growth of ZnO thin films by the atomic layer deposition technique

Abstract

Preferred orientation of ZnO thin films deposited by the atomic layer deposition (ALD) technique could be manipulated by deposition temperature. In this work, diethyl zinc (DEZn) and deionized water (H(2)O) were used as a zinc source and oxygen source, respectively. The results demonstrated that (10.0) dominant ZnO thin films were grown in the temperature range of 155-220 °C. The c-axis crystal growth of these films was greatly suppressed. Adhesion of anions (such as fragments of an ethyl group) on the (00.2) polar surface of the ZnO thin film was believed to be responsible for this suppression. In contrast, (00.2) dominant ZnO thin films were obtained between 220 and 300 °C. The preferred orientations of (10.0) and (00.2) of the ZnO thin films were examined by XRD texture analysis. The texture analysis results agreed well with the alignments of ZnO nanowires (NWs) which were grown from these ZnO thin films. In this case, the nanosized crystals of ZnO thin films acted as seeds for the growth of ZnO nanowires (NWs) by chemical vapor deposition (CVD) process. The highly (00.2) textured ZnO thin films deposited at high temperatures, such as 280 °C, contained polycrystals with the c axis perpendicular to the substrate surface and provided a good template for the growth of vertically aligned ZnO NWs.

Tuning of material properties of ZnO thin films grown by plasma-enhanced atomic layer deposition at room temperature

“…In agreement with our results, on Si(100) substrates, polycrystalline ZnO films with a (100) preferential orientation have been obtained by thermal ALD (using DEZ and water), 14 PE-ALD (using DEZ and O 2 -plasma), 31 and PE-ALD (using DMZ and O 2 -plasma) 35 at 130, 100, and 25 C, respectively. However, a study of thermal ALD (using DEZ and water) at 23 C yielded ZnO with a (002) preferential orientation.…”

“…1 These properties are essential for various applications such as solar cells, 2-4 transparent conductive oxide layers, [5][6][7][8] piezoelectric nanogenerators, [9][10][11][12] and gas sensors. [13][14][15] The ability to tune optical and structural properties of the zinc oxide films is crucial for adapting the material characteristics to meet device requirements (i.e., enhanced device efficiency or sensitivity). [16][17][18] Furthermore, the application of ZnO on thermo-sensitive substrates such as polymers [19][20][21] and biomaterials 22,23 requires deposition processes operating at low temperatures which should be well below the glass transition temperature of polymers and temperatures that would lead to, e.g., degradation of the biomolecules.…”

Direct evidence of ZnO morphology modification via the selective adsorption of ZnO-binding peptides

“…The crystal orientation of ZnO films is controlled by its deposition temperature: 280 C and 165 C being used for the (0001) and (10 10) planes respectively. 85 The as-grown ZnO films were annealed at 800 C (1 hour) prior to the confirmation of crystal orientation by XRD. All substrates studied, ZnO films, silicon wafers, and glass slide, were cleaned with acetone, dried in air, and placed into 12 mL peptide solution prepared in PBS (phosphate buffered saline, 50 mM phosphate and 150 mM NaCl, pH 7.0).…”

Fabrication of ZnO Nanopillars by Atomic Layer Deposition

“…However, when the temperature is above 200 C, the DEZn molecules desorb from the c-Al 2 O 3 surface and the growth rate becomes much less than one monolayer per ALD cycle. 14) We found that when a ZnO seed layer is prepared by ALD on the c-Al 2 O 3 at T ¼ 180 C and heat-treated at a high temperature, the DEZn molecules can be absorbed on the ZnO seeds at T 200 C. This indicates that the surface of ZnO seed layer offers stable absorption sites for DEZn molecules at high growth temperatures. On the other hand, it has been pointed out that at the first 20 cycles in the ALD process, the deposition rate is much smaller than one monolayer per ALD cycle.…”

“…ALD has been used only to deposit a seed layer to grow ZnO nanorods. [12][13][14] Although the nanoscaled control of film thickness is easily achieved by ALD, none have applied ALD to deposit the nanostructures.…”