论文标题

蒸气相外延期间GAN(0001)原子步骤的动力学

Dynamics of Atomic Steps on GaN (0001) during Vapor Phase Epitaxy

论文作者

Ju, Guangxu, Xu, Dongwei, Thompson, Carol, Highland, Matthew J., Eastman, Jeffrey A., Walkosz, Weronika, Zapol, Peter, Stephenson, G. Brian

论文摘要

GAN(0001)表面的形态图像通常显示出半单位高度的步骤,将一系列露台分开,具有交替的大宽度和小宽度。这可以通过Wurtzite晶体结构的$αβαβ$堆叠序列来解释,这导致了最低能量步骤方位角的交替$ a $ a $ a $ a $ a $ a $ a $ a $ a和$ b $ edge的结构,即步骤正常为$ [0 1 \ bar {1} 0] $类型。预测的Adatom附件动力学的差异为$ a $ a $ a $ $ steps将导致交替的$α$和$β$ terrace宽度。但是,由于难以实验确定哪个步骤为$ a $ a或$ b $,因此无法确定其行为的绝对差异,例如哪个步骤具有较高的Adatom附件率常数。在这里,我们表明表面X射线散射可以测量$α$和$β$露台的分数,因此明确区分了$ a $ a $ a $ a $ a和$ b $步骤的增长动态。我们首先介绍了GAN晶体截断杆(CTRS)的强度曲线的计算,这些杆(CTRS)表明对$α$ terrace分数$f_α$明显依赖。然后,我们介绍了通过蒸气相支配在(0001)GAN上同型生长期间进行\ textIt {int intu {原位{原位}的表面X射线散射测量。通过分析$(1 0 \ bar {1} l)$和$(0 1 \ bar {1} l)$ ctrs的形状,我们确定稳态$f_α$以较高的增长率增加,这表明附件率常数在$ a $ a $ a $ a $ a $ a $ a $ sptess。我们还观察到改变生长条件后$f_α$的动态。使用Burton-Cabrera-Frank模型为具有交替步骤类型的表面进行分析,以提取$ a $ a $和$ b $步骤的动力学参数的值。将这些与GAN的预测进行了比较(0001)。

Images of the morphology of GaN (0001) surfaces often show half-unit-cell-height steps separating a sequence of terraces having alternating large and small widths. This can be explained by the $αβαβ$ stacking sequence of the wurtzite crystal structure, which results in steps with alternating $A$ and $B$ edge structures for the lowest energy step azimuths, i.e. steps normal to $[0 1 \bar{1} 0]$ type directions. Predicted differences in the adatom attachment kinetics at $A$ and $B$ steps would lead to alternating $α$ and $β$ terrace widths. However, because of the difficulty of experimentally identifying which step is $A$ or $B$, it has not been possible to determine the absolute difference in their behavior, e.g. which step has higher adatom attachment rate constants. Here we show that surface X-ray scattering can measure the fraction of $α$ and $β$ terraces, and thus unambiguously differentiate the growth dynamics of $A$ and $B$ steps. We first present calculations of the intensity profiles of GaN crystal truncation rods (CTRs) that demonstrate a marked dependence on the $α$ terrace fraction $f_α$. We then present surface X-ray scattering measurements performed \textit{in situ} during homoepitaxial growth on (0001) GaN by vapor phase epitaxy. By analyzing the shapes of the $(1 0 \bar{1} L)$ and $(0 1 \bar{1} L)$ CTRs, we determine that the steady-state $f_α$ increases at higher growth rate, indicating that attachment rate constants are higher at $A$ steps than at $B$ steps. We also observe the dynamics of $f_α$ after growth conditions are changed. The results are analyzed using a Burton-Cabrera-Frank model for a surface with alternating step types, to extract values for the kinetic parameters of $A$ and $B$ steps. These are compared with predictions for GaN (0001).

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