Search

The structural characteristics, chemical composition, and element spatial distribution in MgxZn1-xO ceramics were investigated using X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, energy-dispersive X-ray spectroscopy, and cathodoluminescence techniques. The study revealed that the morphology of the ceramic samples, as well as the mechanism of solid solution formation, depend on the relative contribution of both oxides in the charge. It was discovered that hexagonal and cubic phases of the solid solution were found to form simultaneously. An increase in the MgO content in the charge results in the magnesium content rise in the hexagonal grains continuously, reaching approximately 13 at.%. It was discovered an enrichment of grain boundaries with zinc and magnesium playing a significant role in doping ZnO and MgO grains. Obtained results allowed to propose two mechanisms involved in the formation of solid solution ceramics: i) diffusion of Mg and Zn along grain boundaries, followed by their incorporation into ZnO or MgO grains, respectively, and ii) interdiffusion of Mg into ZnO and Zn into MgO due to direct contact of ZnO and MgO grains. The second mechanism appears to dominate when both ZnO and MgO contribute comparably, increasing the probability of their direct contact. This study significantly advances the understanding of the process of the formation of MgxZn1-xO ceramics under thermodynamic conditions. These insights are crucial for optimizing the doping process and improving the material properties, thereby promoting innovations in the ceramics industry.

Optical control of spins in condensed matter systems such as semiconductor nanostructures requires precise knowledge of the polarization properties of the associated optical transitions subject to an external magnetic field. Here, we demonstrate that coherent optical spectroscopy in the form of photon echoes can be successfully used to evaluate the magnetic anisotropies of valence-band states. It manifests in drastic changes of the transient signals when the orientation of the magnetic field with respect to the crystallographic axes is varied. In particular, we use the two-pulse spin-dependent photon echo to study the in-plane hole spin anisotropy in a 20-nm-thick CdTe/Cd_{0.76}Mg_{0.24}Te single quantum well by exciting the donor-bound exciton resonance. We take advantage of the photon echo sensitivity to the relative phase of the electron and hole spin precession in the ground and excited states, respectively, and study various interactions contributing to the hole in-plane spin properties. The main contribution is found to arise from the crystal cubic symmetry described by the Luttinger parameter q=0.095±0.005, which is substantially larger than the one theoretically expected for CdTe or found in other quantum well structures. Another contribution is induced by the strain within the quantum well. These two contributions lead to different harmonics of the spin precession frequencies in the photon echo experiment, when the strength and orientation of the Voigt magnetic field are varied. The magnitude of the effective in-plane hole g factor is found to vary in the range |g_{h}[over ̃]|=0.125–0.160 in the well plane.

We report on the fabrication and characterization of a new type of mid-infrared photodetector. The infrared sensitive element of the detector is a PbSe single quantum well (SQW) embedded in an intrinsic region of a CdTe p-i-n diode. Electron-beam-induced current (EBIC) measurements confirm the location of the PbSe SQW near the middle of the intrinsic CdTe layer. The measured diffusion length of minority carriers of about 0.5 μm allows effective collecting of the photoexcited carriers in the highly doped regions of the diodes. The PbSe/CdTe heterostructures exhibit a strong photosensitivity in the mid-infrared spectral region. Photo-response measurements show abnormal temperature dependence of the photosensitivity. The photo-response signal increases with decreasing temperature reaching a maximum at about 170 K and upon a further decrease in temperature the signal weakens and vanishes at about 100 K. Current-voltage measurements demonstrate very good junction characteristics with a rectifying ratio of 585 at ± 0.5 V and an ideality factor of 1.05 at room temperature. Possible mechanisms of carrier transport trough the junction are discussed.

The new type of a p-i-n structure consists of a single acceptor doped ZnO:N film grown by plasma assisted molecular beam epitaxy, a thin isolating Al2O3 layer grown by atomic layer deposition method and n-type GaN template. The maximum forward-to-reverse current ratio IF/IR in the obtained diode is about 8   ×   106 at  ±7 V. Electron-beam-induced current measurements confirmed the presence of a p-i-n junction and the presence of the isolating layer located at the p-ZnO/n-GaN interface. The diffusion length of carriers was calculated. The heterostructure exhibits an absorption in the UV range and the ratio between light (UV) and dark current is above four orders of magnitude. [ABSTRACT FROM AUTHOR]

We study nanoscale morphology of PbTe/CdTe multilayer heterostuctures grown by molecular beam epitaxy on hybrid GaAs/CdTe (100) substrates. Nominally, the structures consist of 25 repetitions of subsequently deposited CdTe and PbTe layers with comparable thicknesses of 21 and 8 nm, respectively. However, the morphology of the resulting structures crucially depends on the growth temperature. The two-dimensional layered, superlattice-like character of the structures remains preserved only when grown at low substrate temperatures, such as 230 °C. The samples grown at the slightly elevated temperature of 270 °C undergo a morphological transformation to structures consisting of CdTe and PbTe pillars and columns oriented perpendicular to the substrate. Although the pillar-like objects are of various shapes and dimensions these structures exhibit exceptionally strong photoluminescence in the near infrared spectral region. At the higher growth temperature of 310 °C, PbTe and CdTe separate completely forming thick layers oriented longitudinally to the substrate plane. The observed topological transformations are driven by thermally activated atomic diffusion in the solid state phase. The solid state phase remains fully coherent during the processes. The observed topological transitions leading to the material separation in PbTe/CdTe system could be regarded as an analog of spinodal decomposition of an immiscible solid state solution and thus they can be qualitatively described by the Cahn–Hillard model as proposed by Groiss et al (2014 APL Mater.2 012105). [ABSTRACT FROM AUTHOR]