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The ceramics based on cubic (Zr0.82–xHfxY0.17Eu0.01)O0.91 with different contents of hafnium were studied. In the work, the elemental composition of the samples was obtained, the cathodoluminescence (CL) spectra and decay kinetics of europium luminescence were studied. The researched showed increase in the content of hafnium doesn't affect the position and number of observed bands in the luminescence spectrum. The electric dipole and magnetic dipole radiative transitions ratio was estimated for all samples. It's demonstrated that a decrease in the local symmetry of the europium ion associated with an increase in the hafnium content. It's shown the 5D0–1F1 transition Eu3+ decay time doesn't depend on the hafnium content, but v-aries significantly in different regions of the sample, which can be attributed to the influence of grain bou-ndaries. [ABSTRACT FROM AUTHOR]

We present a cathodoluminescence (CL) and superconducting quantum interference device (SQUID) magnetometry study of the generation of ferromagnetism (FM) in GaN doped with non-magnetic (copper) and magnetic (manganese) impurities. Our results suggest that p–d hybridization between Cu and N ions promotes FM in GaN:Cu, and that an exchange interaction between the Cu2+ (d9) orbitals and the t2g anti-bonding orbitals of Mn2+ ions generates FM in GaN:Cu and GaN:Mn. Besides that, the exchange interaction is mediated by holes, created by the acceptor nature of the impurities Cu2+ and Mn2+, and of the point-defects-type gallium vacancies (VGa) present in samples. For this study, we synthesized undoped GaN, GaN:Cu, and GaN:Mn samples by thermal evaporation onto Ni0.8Cr0.2/Si substrates in a horizontal furnace operated at low vacuum. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the obtained samples consisted of GaN without residual oxide phases. XPS measurements also revealed the coexistence of Cu+ and Cu2+ ions in the GaN:Cu sample, and Mn2+ in the GaN:Mn sample. CL spectra from Cu and Mn-doped GaN samples showed that doping generates a relative intensity enhancement of two bands centered at 2.60 and 3.00 eV, associated with the formation of VGa in GaN. Magnetization–applied field (M–H) curves of the GaN, GaN:Cu, and GaN:Mn samples revealed a FM behavior at room temperature. [ABSTRACT FROM AUTHOR]

The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25–310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm−1) to be defined (0.5 A mm−1 at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current. [ABSTRACT FROM AUTHOR]