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DDC: 530 × Publisher: Weinheim : Wiley-VCH × search.filters.applied.f.series: Physica status solidi : B, Basic research 258 (2021), Nr. 11 ×

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    Weak electron irradiation suppresses the anomalous magnetization of N-doped diamond crystals
    (Weinheim : Wiley-VCH, 2021) Setzer, Annette; Esquinazi, Pablo D.; Daikos, Olesya; Scherzer, Tom; Pöppl, Andreas; Staacke, Robert; Lühmann, Tobias; Pezzagna, Sebastien; Knolle, Wolfgang; Buga, Sergei; Abel, Bernd; Meijer, Jan
    Several diamond bulk crystals with a concentration of electrically neutral single substitutional nitrogen atoms of ≲80 ppm, the so-called C or P1 centers, are irradiated with electrons at 10 MeV energy and low fluence. The results show a complete suppression of the irreversible behavior in field and temperature of the magnetization below 30 K, after a decrease in ≲40 ppm in the concentration of C centers produced by the electron irradiation. This result indicates that magnetic C centers are at the origin of the large hysteretic behavior found recently in nitrogen-doped diamond crystals. This is remarkable because of the relatively low density of C centers, stressing the extraordinary role of the C centers in triggering those phenomena in diamond at relatively high temperatures. After annealing the samples at high temperatures in vacuum, the hysteretic behavior is partially recovered.
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    Temperature Dependence of Dark Spot Diameters in GaN and AlGaN
    (Weinheim : Wiley-VCH, 2021) Netzel, Carsten; Knauer, Arne; Brunner, Frank; Mogilatenko, Anna; Weyers, Markus
    Threading dislocations in c-plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called “dark spots.” These areas are observable in luminescence measurements with spatial resolution in the submicrometer range. Dark spots reduce the internal quantum efficiency in single layers and light-emitting devices. In cathodoluminescence measurements, the diameter of dark spots (full width at half maximum [FWHM]) is observed to be 200–250 nm for GaN. It decreases by 30–60% for AlxGa1−xN with x ≈ 0.5. Furthermore, the dark spot diameter increases with increasing temperature from 83 to 300 K in AlGaN, whereas it decreases in GaN. Emission energy mappings around dark spots become less smooth and show sharper features on submicrometer scales at low temperature for AlGaN and, on the contrary, at high temperature for GaN. It is concluded that charge carrier localization dominates the temperature dependence of dark spot diameters and of the emission energy distribution around threading dislocations in AlGaN, whereas the temperature-dependent excitation volume in cathodoluminescence and charge carrier diffusion limited by phonon scattering are the dominant effects in GaN. Consequently, with increasing temperature, nonradiative recombination related to threading dislocations extends to wider regions in AlGaN, whereas it becomes spatially limited in GaN.