Evolution of the m-Plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure
Evolution of the m-Plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure
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DOI：
10.1021/acs.cgd.6b01281
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发表时间：
2017-02-01
影响因子：
3.8
通讯作者：
Shields, Philip A.
中科院分区：
文献类型：
--
作者：
Coulon, Pierre-Marie;Vajargah, Shahrzad Hosseini;Shields, Philip A.
由于GaN/InGaN核壳纳米棒的侧壁不存在极化相关电场，缺陷密度较低，发射体积较大，自由表面的应变弛豫较大，因此在光电子学领域具有广阔的应用前景。核壳结构允许生长更厚的InGaN壳层，这将提高发光二极管的效率。然而，金属有机气相外延生长这种薄膜的方式却鲜为人知。通过纳米制造、外延生长和详细的表征相结合，本工作揭示了InGaN外延壳的生长模式的演变，从二维(2D)生长模式到三维(3D)条纹生长模式，并且没有随着层厚的增加而形成额外的线缺陷。铟分布的测量显示出沿方向的波动，低铟组分和高铟组分分别与2D和3D生长模式有关。在GaN/InGaN核壳界面处观察到原子台阶的出现频率与在2D层内观察到的沿[0001]方向的准周期铟波动的频率相似，从而提供了在台阶处产生的局部应变释放是通过弹性弛豫来触发生长模式改变的证据。这项研究表明，使用预刻蚀的GaN纳米棒可以避免在生长更宽的InGaN壳层过程中产生失配位错。值得注意的是，这使得基于吸收的器件和发光二极管的增长成为可能，它们的发射层足够宽，以缓解效率下降。
GaN/InGaN core-shell nanorods are promising for optoelectronic applications due to the absence of polarization-related electric fields on the sidewalls, a lower defect density, a larger emission volume, and strain relaxation at the free surfaces. The core-shell geometry allows the growth of thicker InGaN shell layers, which would improve the efficiency of light emitting diodes. However, the growth mode of such layers by metal organic vapor phase epitaxy is poorly understood. Through a combination of nanofabrication, epitaxial growth, and detailed characterization, this work reveals an evolution in the growth mode of InGaN epitaxial shells, from a two-dimensional (2D) growth mode to three-dimensional (3D) striated growth without additional line defect formation with increasing layer thickness. Measurements of the indium distribution show fluctuations along the directions, with low and high indium composition associated with the 2D and 3D growth modes, respectively. Atomic steps at the GaN/InGaN core-shell interface were observed to occur with a similar frequency as quasi-periodic indium fluctuations along [0001] observed within the 2D layer, to provide evidence that the resulting local strain relief at the steps acts as the trigger for a change of growth mode by elastic relaxation. This study demonstrates that misfit dislocation generation during the growth of wider InGaN shell layers can be avoided by using pre-etched GaN nanorods. Significantly, this enables the growth of absorption-based devices and light-emitting diodes with emissive layers wide enough to mitigate efficiency droop.