Nitrogen Mediated Crystallization Research Articles

Effect of nanoscale inhomogeneity on blocking temperature of ZnO:Co films fabricated by using nitrogen-mediated crystallization

Effect of nanoscale inhomogeneity on blocking temperature of ZnO:Co films fabricated by using nitrogen-mediated crystallization

Improved GZO Thin Film Structures by Nitrogen-Mediated Crystallization Process to Apply to Touch Sensing

Improved GZO Thin Film Structures by Nitrogen-Mediated Crystallization Process to Apply to Touch Sensing

Control of inhomogeneity and magnetic properties of ZnO:Co films grown by magnetron sputtering using nitrogen

We experimentally report the control of structural inhomogeneity and magnetic properties of Co-doped ZnO films using nitrogen mediated-crystallization. The ZnO:CoN were grown on a silicon substrate at room temperature by RF-magnetron sputtering using nitrogen and followed by a post-annealing treatment for 3 hours at 400 °C, 600 °C, 800 °C and 1000 °C in the air. This method induces changes in inhomogeneity properties comprised by microstructure and stoichiometry of each film, which are confirmed by X-ray diffraction, thermal desorption, and X-ray fluorescence measurements. The difference in inhomogeneity has led to the transformation in the magnetic properties. Films annealed at 400 °C, which showed the highest inhomogeneity, exhibited superparamagnetic-ferromagnetic properties. In contrast, all the other films exhibited diamagnetic properties. Increasing the post-annealing temperature above 400 °C reduces inhomogeneities indicated by improved grain size, decreased impurities, and lattice parameters and stoichiometry of ZnO:CoN films approached those of pure ZnO. Our present results will contribute to control the inhomogeneity of ZnO:Co films to improve magnetic properties at room temperature.

Improved Nanoscale Al-Doped ZnO with a ZnO Buffer Layer Fabricated by Nitrogen-Mediated Crystallization for Flexible Optoelectronic Devices

To achieve excellent semiconductor device performance, especially for low-temperature processing of semiconductors, the need to devise strategies to engineer the surface and interface and to develop characterization techniques to understand the cause-effect relationship of surface and interface of semiconductor devices remains to be a key issue. Here, we present a nucleation control method, termed nitrogen-mediated crystallization (NMC), to engineer the surface morphology of a ZnO buffer layer and analyze first- and second-degree statistical surfaces to reveal the morphological relationship between the buffer layer and the buffered AZO film. The surface parameter is generally understood as the surface roughness (roughness average or RMS roughness) or the surface height profile, and our experimental results suggest that the physical properties of the buffered AZO films are strongly influenced by the uniformity of the fractal geometry of the buffer layers and are insensitive to their surface roughness. We d...

Effects of sputtering gas pressure dependence of surface morphology of ZnO films fabricated via nitrogen mediated crystallization

ZnO films were fabricated by RF magnetron sputtering with nitrogen mediated crystallization (NMC) under various gas pressures. X-ray diffraction measurements show that the NMC-ZnO films are highly crystalline regardless of the gas pressure, and the full width at half maximum values of the (0002) rocking curves range from 0.032 to 0.044°. In contrast, atomic force microscopy (AFM) reveals that the gas pressure plays an important role in determining the surface morphology of the films. The root-mean-square (RMS) roughness decreases monotonically from 1.05 to 0.60 nm with increasing pressure from 0.2 to 0.7 Pa. However, the RMS roughness increases with further increases in the pressure, reaching 2.15 nm at 2.1 Pa. The height distribution of the NMC-ZnO films derived from the AFM images is narrowest at 0.7 Pa, indicating that the smooth surface obtained at 0.7 Pa can be attributed to spatially uniform nucleation occurring in a short time period. These results indicate that the sputtering gas pressure is a key parameter for controlling the surface morphology of NMC-ZnO films.

Effects of morphology of buffer layers on ZnO/sapphire heteroepitaxial growth by RF magnetron sputtering

ABSTRACTEffects of surface morphology of buffer layers on ZnO/sapphire heteroepitaxial growth have been investigated by means of “nitrogen mediated crystallization (NMC) method”, where the crystal nucleation and growth are controlled by absorbed nitrogen atoms. We found a strong correlation between the height distribution profile of NMC-ZnO buffer layers and the crystal quality of ZnO films. On the buffer layer with a sharp peak in height distribution, a single-crystalline ZnO film with atomically-flat surface was grown. Our results indicate that homogeneous and high-density nucleation at the initial growth stages is critical in heteroepitaxy of ZnO on lattice mismatched substrates.

Growth mechanism of ZnO deposited by nitrogen mediated crystallization

We investigate the growth mechanism of ZnO deposited by a nitrogen mediated crystallization (NMC) method. NMC is a method in which nitrogen is used to control nucleation via a nitrogen adsorption–desorption behavior. The growth of NMC-ZnO is classified into three stages, that is, the pre-nucleation stage, nucleation and grain growth stage for 4–30 nm in thickness, and coalescence stage for 31–100 nm in thickness. NMC-ZnO nucleation takes place in a very short period compared to that for conventional ZnO. Hence, NMC-ZnO has a uniform grain size distribution, flat surface with less spiky grains, and a longer lateral correlation length of the surface, leading to a larger grain size than in conventional ZnO. Utilizing this NMC-ZnO as a buffer layer, low resistive aluminum doped zinc oxide ZnO:Al (AZO) films are obtained at the buffer layer film thickness ranging from 4 to 30 nm. The lowest resistivity is 3.4 × 10−4 Ω cm for 90 nm thick AZO deposited on NMC-ZnO buffer layers of 10 and 30 nm in thickness.

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing an off-axis sputtering configuration together with buffer layers prepared via nitrogen-mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and, thus, to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two-dimensional growth of subsequently grown ZnO films, being particularly enhanced by employing an off-axis sputtering configuration in which the substrate is positioned out of the high-energy particles, such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and a high electron mobility of 88 cm2/V·s are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high-quality epitaxial ZnO films.

Epitaxial Growth of ZnInON Films with Tunable Band Gap from 1.7 to 3.3 eV on ZnO Templates

Epitaxial ZnInON (ZION) films with a tunable band gap have been successfully fabricated by RF magnetron sputtering on ZnO templates prepared via nitrogen mediated crystallization (NMC). X-ray diffraction (XRD) measurements show that the full widths at half maximum of the rocking curves from (002) and (101) planes are small at 0.10 and 0.08°, respectively, indicating a high crystallinity with good in-plane and out-of-plane alignments. Since the coherent growth of 35-nm-thick ZION films on NMC-ZnO templates is deduced from the reciprocal space mapping around the (105) diffraction, there is little lattice relaxation at the interface between the films and templates, which is significant in terms of the suppression of carrier recombination. The band gap of the ZION films has been tuned in a wide range of 1.7–3.3 eV by changing the Zn:In ratio. These results indicate that ZION is a potential absorption layer material of solar cells.

Effects of Hydrogen Dilution on ZnO Thin Films Fabricated via Nitrogen-Mediated Crystallization

Hydrogenated ZnO thin films have been successfully deposited on glass substrates via a nitrogen mediated crystallization (NMC) method utilizing RF sputtering. Here we aim to study the crystallinity and electrical properties of hydrogenated NMC-ZnO films in correlation with substrate temperature and H2 flow rate. XRD measurements reveal that all the deposited films exhibit strongly preferred (001) orientation. The integral breadth of the (002) peak from the hydrogenated NMC-ZnO films is smaller than that of the conventional hydrogenated ZnO films fabricated without nitrogen. Furthermore, the crystallinity and surface morphology of the hydrogenated NMC-ZnO films are improved by increasing substrate temperature to 400 °C, where the smallest integral breadth of (002) 2θ–ω scans of 0.83° has been obtained. By utilizing the hydrogenated NMC-ZnO films as buffer layers, the crystallinity of ZnO:Al (AZO) films is also improved. The resistivity of AZO films on NMC-ZnO buffer layers decreases with increasing H2 flow rate during the sputter deposition of buffer layers from 0 to 5 sccm. At a H2 flow rate of 5 sccm, 20-nm-thick AZO films with low resistivity of 1.5×10-3 Ω cm have been obtained.

Crystallinity control of sputtered ZnO films by utilizing buffer layers fabricated via nitrogen mediated crystallization: Effects of nitrogen flow rate

High quality ZnO:Al (AZO) films have been obtained by utilizing buffer layers fabricated via nitrogen mediated crystallization (NMC), where sputtering method is employed for preparation of both buffer layers and AZO films. Introduction of small amount of N2 (N2/(Ar+N2) = 16%) to the sputtering atmosphere of NMC-ZnO buffer layers drastically improves the crystallinity of buffer layers and thus AZO films. The most remarkable effect of the buffer layers is a significant reduction in the resistivity at high base pressure of background gases. The resistivity of conventional AZO films increases from 2.0 m O•cm to 70.0 O•cm with increasing the base pressure from 3×10-5 Pa to 1×10-3 Pa, while the resistivity of AZO films with NMC buffer layers increases from 0.5 mO•cm to 2.0 mO•cm, where the thickness of AZO film is 88 nm. Furthermore, AZO films with a sheet resistance of 10O/? and an optical transmittance higher than 80% in a wide wavelength range of 400–1100 nm have been obtained.

ZnO:Al Thin Films with Buffer Layers Fabricated via Nitrogen Mediated Crystallization: Effects of N<sub>2</sub>/Ar Gas Flow Rate Ratio

ZnO:Al Thin Films with Buffer Layers Fabricated via Nitrogen Mediated Crystallization: Effects of N<sub>2</sub>/Ar Gas Flow Rate Ratio