Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, No. 1, section 4, Roosevelt Road, Taipei, 10617 Taiwan.
Nanotechnology. 2019 Jul 5;30(27):275201. doi: 10.1088/1361-6528/ab128e. Epub 2019 Mar 22.
An AlGaN/GaN multi-shell structure on a GaN nanorod (NR) is formed by using the self-catalytic pulsed growth process of metalorganic chemical vapor deposition with Ga and Al/N supplies in the first and second half-cycles, respectively. With Al supply, a thin AlGaN layer is precipitated near the end of a growth cycle to form the AlGaN/GaN structure. Because of the lower chemical potential for GaN nucleation, when compared with AlN, a GaN layer is first deposited in a growth cycle. AlGaN is not precipitated until the AlN nucleation probability becomes higher when the catalytic Ga droplet is almost exhausted. Because the Al adatoms on the NR sidewalls hinder the upward migration of Ga adatoms for contributing to the Ga droplet at the NR top, the size of the Ga droplet decreases along growth cycle leading to the decrease of GaN layer thickness at the top until a steady state is reached. In this process, the slant facet of an NR changes from the (1-102)-plane into (1-101)-plane. To interpret the observed growth behaviors, formulations are derived for theoretically modeling the AlN nucleation probability, NR height increment in each growth cycle, and the time of exhausting the Ga droplet in a cycle.
在 GaN 纳米棒（NR）上形成了 AlGaN/GaN 多壳结构，这是通过使用金属有机化学气相沉积的自催化脉冲生长工艺，在第一和第二个半周期中分别使用 Ga 和 Al/N 作为源来实现的。在 Al 供应的情况下，在生长循环的末端附近沉淀出一层薄的 AlGaN 层，从而形成 AlGaN/GaN 结构。由于 GaN 成核的化学势较低，与 AlN 相比，在生长循环中首先沉积 GaN 层。只有当催化 Ga 液滴几乎耗尽时，AlN 成核的概率变得更高，AlGaN 才会沉淀。由于 NR 侧壁上的 Al adatoms 阻碍了 Ga adatoms 的向上迁移，从而有助于 NR 顶部的 Ga 液滴，因此随着生长循环的进行，Ga 液滴的尺寸减小，导致顶部 GaN 层厚度减小，直到达到稳定状态。在这个过程中，NR 的斜角从（1-102）-面变为（1-101）-面。为了解释观察到的生长行为，推导了理论模型的公式，用于模拟 AlN 成核概率、每个生长循环中 NR 的高度增量以及液滴在一个循环中耗尽的时间。
