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 Al_xGa_1−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.

中文翻译：

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GaN 和 AlGaN 中暗点直径的温度依赖性

c 面 (Al,Ga)N 层中的穿透位错被发光效率降低的区域包围，称为“暗点”。这些区域在具有亚微米范围的空间分辨率的发光测量中是可观察到的。黑点降低了单层和发光器件的内部量子效率。在阴极发光测量中，观察到 GaN 的暗点直径（半高全宽 [FWHM]）为 200-250 nm。对于 Al _x Ga _{1− x} N，它减少了 30–60% ，x ≈ 0.5。此外，在 AlGaN 中，暗点直径随着温度从 83 K 增加到 300 K 而增加，而在 GaN 中则减小。在低温下，对于 AlGaN，暗点周围的发射能量映射变得不那么平滑，并在亚微米尺度上显示出更清晰的特征，相反，在高温下，对于 GaN 来说。得出的结论是，电荷载流子局部化支配着 AlGaN 中暗点直径和穿透位错周围的发射能量分布的温度依赖性，而阴极发光中的温度依赖性激发体积和受声子散射限制的电荷载流子扩散是 GaN 中的主要影响. 因此，随着温度的升高，与穿透位错相关的非辐射复合扩展到 AlGaN 中更宽的区域，