Kusaba Akira, Li Guanchen, von Spakovsky Michael R, Kangawa Yoshihiro, Kakimoto Koichi
Department of Aeronautics and Astronautics, Kyushu University, Fukuoka 819-0395, Japan.
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
Materials (Basel). 2017 Aug 15;10(8):948. doi: 10.3390/ma10080948.
Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and N-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on N-H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches.
清晰理解依赖于表面重构的基本生长过程对于更精确地控制气相外延至关重要。在本研究中，使用最陡熵升量子热力学（SEAQT）研究了金属有机气相外延（MOVPE）条件下（2×2晶胞上的3Ga-H和N-H + Ga-H）氨在GaN(0001)重构表面上的化学吸附。SEAQT是一个基于热力学系综的第一性原理框架，它可以预测非平衡过程的行为，甚至是那些远离平衡的过程，在这些过程中状态演化是可逆和不可逆动力学的组合。由于化学吸附过程从高度非平衡状态开始，SEAQT是从第一性原理基础上处理这个问题的理想选择。分析结果表明，在3Ga-H上吸附的概率显著高于在N-H + Ga-H上吸附的概率。此外，还确定了这些吸附概率对生长温度的依赖性以及反应热导致的温度升高。所应用的非平衡热力学建模可以通过选择更优的重构表面来更好地控制MOVPE过程。该建模还证明了DFT-SEAQT耦合在确定详细的非平衡过程特征方面的有效性，其计算负担比基于力学的微观-介观方法要小得多。
