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We investigated the glide velocities of 30° Si-core partial dislocations for the expansion of double-Shockley stacking faults (DSFs) in heavily nitrogen-doped 4H-SiC crystals at high temperatures of approximately 1000 °C. The heavily doped epilayers grown by chemical vapor deposition were successively annealed. The expansion of DSFs in the heavily doped epilayers was tracked by a photoluminescence (PL) imaging technique. From the PL images obtained after each annealing treatment, the glide velocities of the 30° Si-core partial dislocations were estimated. In particular, temperature dependence and nitrogen-concentration dependence of the dislocation velocities were obtained. We also report the influence of the strain energies of the bounding dislocations on the velocities. Based on the experimental results, the quantitative expression of the dislocation glide is discussed. [ABSTRACT FROM AUTHOR]

We investigated the structures and expansion behavior of double-Shockley stacking faults (DSFs) formed in heavily nitrogen-doped 4H-SiC during annealing. Heavily doped epilayers prepared as specimens were successively annealed. Various types of DSFs showing different shapes and dislocation contrasts were found in photoluminescence and synchrotron X-ray topography images. Taking account of every possible stacking sequence forming DSFs, the structures of various types of DSFs were determined from observations by plan-view transmission electron microscopy (TEM) and cross-sectional high-angle annular dark-field scanning TEM. We found that a bounding dislocation enclosing a DSF splits into two partial dislocations (PDs), and their Burgers vectors are identical, while the distance of the two PDs depended on their core structures (30° Si-, 30° C- or 90° C-core). We also discussed the contrast rule for the dislocation consisting of two PDs in the synchrotron X-ray topography images and the mobile PDs for the DSF expansion in the epilayers with different nitrogen concentrations. [ABSTRACT FROM AUTHOR]

The formation and evolution of defects in 4H-SiC Schottky barrier diode high-energy particle detectors have been investigated and correlated with the detectors' properties. Low temperature annealing at 300 °C is found to significantly recover the charge collection efficiency as degraded by 1 MeV electron irradiation. At higher temperatures, an anneal-induced degradation in the detector's performance is observed. Current-voltage, capacitance-voltage, and deep level transient spectroscopy (DLTS) measurements are used to ascertain the effect of defects on the detector performance. The latter reveals that the DLTS defect levels, EH1 and EH3, are related to the initial recovery of the charge collection efficiency. [ABSTRACT FROM AUTHOR]

The Brønsted acid–base reaction between 3-hydroxy-2-quinoxalinecarboxylic acid (Hhqxc) and imidazole (Im) in acetone–H2O yielded two 1 : 1 salts: anhydrous (HIm+)(hqxc−) (1) and hydrated (HIm+)(hqxc−)·(H2O) (2), where HIm+ and hqxc− are imidazolium and 3-hydroxy-2-quinoxalinecarboxylate, respectively. Single-crystal X-ray structural analyses and vibrational spectra were consistent with the lactam tautomer of the hqxc− anion, which formed π-dimers in both 1 and 2. Each π-dimer in crystal 1 was connected by intermolecular N–H…O hydrogen-bonding interactions to form a linear hqxc− chain, whereas the π-dimers in crystal 2 formed an intermolecular N–H…O hydrogen-bonding zigzag chain. The HIm+ cations existed in the crystalline space between the hydrogen-bonding hqxc− anionic chains. A reversible crystal-to-crystal structural transformation between crystals 1 and 2 was observed following H2O adsorption–desorption, which was confirmed by powder X-ray diffraction measurements, single-crystal X-ray structural analyses, and H2O adsorption–desorption isotherms at 323 K. The structural rearrangement of the hqxc− anions was achieved through changes in the intermolecular hydrogen-bonding interactions. The temperature- and frequency-dependent dielectric constants of crystal 2 revealed a dielectric peak at ~330 K owing to thermal fluctuations of H2O molecules within the crystal. [ABSTRACT FROM AUTHOR]