The presented article concerns the comparison between two different zinc-oxide structures - bulk crystals and polycrystalline thin films. Bulk crystals were grown by a Bridgman method. For thin-film production, a sol-gel spin-coated method was chosen. A part of thin layers samples was annealed in 600 $$^{o}$$ o C to induce recrystallization. The morphological and structural properties of all samples were investigated using various microscopy techniques, X-ray diffraction, and Raman spectroscopy. Confocal and scanning electron microscopy, as well as XRD, was used to estimate the influence of the recrystallization process on the morphology of the samples. The Raman vibrations in different scattering geometries were determined using polarized Raman spectra. What is more, in the case of the non-annealed sol-gel layer, the localized reorientation of crystallites was observed, using Raman microscopy. The morphology of the samples was compared to their optical properties, which were investigated by exploiting UV-Vis absorption and photoluminescence spectroscopy. Absorption spectroscopy allowed us to estimate the energy bandgap for different types of ZnO layers and to compare the values obtained for the ZnO crystal structure obtained by the Bridgman method. The photoluminescence and Raman spectroscopy were used to determine the possible defects correlated with the growth conditions.
Carbon doped GaN crystals grown by hydride vapor phase epitaxy have been investigated using mid-infrared and near-ultraviolet absorption spectroscopy. Two local vibrational modes (LVMs) at 1679 cm−1 and 1718 cm−1 as well as an absorption shoulder in front of the band edge absorption of GaN are discovered, all of which increase in intensity with the carbon concentration. The LVMs are similar in wavenumber position to an LVM formerly observed in carbon-rich AlN crystals and unambiguously assigned to a tri-carbon defect. Together with the polarization dependence of the LVMs, we conclude that in GaN the underlying defects are two crystallographically inequivalent configurations of each three nearest neighbor carbon atoms. The strength of both the infrared and ultraviolet absorption features implies concentrations of the underlying defects of the same order as the total carbon concentration. Hence, the tri-carbon defects contribute to the UV absorption and possess deep energy levels in GaN.
Preparing structures with the sol-gel method often requires control of the basal plane of crystallites, crystallite structures, or the appearance of the voids. One of the critical factors in the formation of a layer are additives, such as aminoalcohols, which increase the control of the sol formation reaction. Since aminoalcohols differ in boiling points and alkalinity, their selection may play a significant role in the dynamics of structure formation. The main aim of this work is to examine the properties of ZnO layers grown using different aminoalcohols at different concentration rates. The layers were grown on various substrates, which would provide additional information on the behavior of the layers on a specific substrate, and the mixture was annealed at a relatively low temperature (400 °C). The research was conducted using monoethanolamine (MEA) and diethanolamine (DEA). The aminoalcohols were added to the solutions in equal concentrations. The microscopic image of the structure and the size of the crystallites were determined using micrographs. X-ray diffractometry and Raman spectroscopy were used for structural studies, phase analysis and to establish the purity of the obtained films. UV-vis absorption and photoluminescence were used to evaluate structural defects. This paper shows the influence of the stabilizer on the morphology of samples and the influence of the morphology and structure on the optical properties. The above comparison may allow the preparation of ZnO samples for specific applications.
In this paper, an overview of the influence of various modifications on ZnO-based RRAM has been conducted. Firstly, the motivation for creating new memory technology is presented. The resistive switching mechanism is explained, including its response to the selection of active layers and electrodes. A comparison of ZnO devices assembled via different deposition methods is made. Additional treatment of the active layer and electrodes improving the performance are reported. This work gives an overview of the influence of different dopants on the characteristics of the device. The manuscript overviews the previous investigation of inclusion of inserting layers and nanostructures into ZnO-based RRAM.
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