Sinito C, Corfdir P, Pfüller C, Gao G, Bartolomé J, Kölling S, Rodil Doblado A, Jahn U, Lähnemann J, Auzelle T, Zettler J K, Flissikowski T, Koenraad P, Grahn H T, Geelhaar L, Fernández-Garrido S, Brandt O
Paul Drude Institut für Festkörperelektronik , Leibniz Institut im Forschungsverbund Berlin e.V. , Hausvogteiplatz 5-7 , 10117 Berlin , Germany.
Department of Applied Physics , TU Eindhoven , Den Dolech 2 , 5612 Eindhoven , AZ , The Netherlands.
Nano Lett. 2019 Sep 11;19(9):5938-5948. doi: 10.1021/acs.nanolett.9b01521. Epub 2019 Aug 14.
Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light-emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection, and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense light emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al-deficient core and an Al-rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.
通过利用纳米线异质结构，展现出高结构完整性并改善光提取，平面（铝，镓）氮基深紫外发光二极管的几个关键问题可能会得到解决。在此，我们研究了通过等离子体辅助分子束外延在硅（111）上生长的氮化镓/（铝，镓）氮纳米线阵列的自发发射。这些纳米线包含单个氮化镓量子盘，其嵌入在长的（铝，镓）氮纳米线段中，这对于有效光提取至关重要。发现这些量子盘在出乎意料的高能量下表现出强烈的发光，即显著高于氮化镓带隙，并且几乎与盘的厚度无关。对纳米线的实际结构和成分进行深入研究后发现，沿着纳米线以及横跨纳米线都自发形成了铝梯度，从而形成了一种复杂的核/壳结构，其核中铝含量不足，而壳中铝含量丰富，且在（铝，镓）氮段的整个长度上铝含量不断变化。沿着纳米线生长轴的这种成分变化会引起壳层的极化掺杂，从而在盘中产生简并电子气，进而屏蔽内建电场。高载流子密度不仅导致了出乎意料的高跃迁能量，还导致辐射寿命仅微弱地依赖于温度，从而使氮化镓量子盘在室温下具有相对较高的内量子效率。
