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Materials 2017, 10(8), 948; https://doi.org/10.3390/ma10080948

Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics

1
Department of Aeronautics and Astronautics, Kyushu University, Fukuoka 819-0395, Japan
2
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
3
Center for Energy Systems Research (CESR), Mechanical Engineering Department, Virginia Tech, Blacksburg, VA 24061, USA
4
Research Institute for Applied Mechanics (RIAM), Kyushu University, Fukuoka 816-8580, Japan
5
Center for Integrated Research of Future Electronics (CIRFE), Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Nagoya 464-8601, Japan
*
Author to whom correspondence should be addressed.
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 11 August 2017 / Published: 15 August 2017
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Abstract

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 Nad-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 Nad-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. View Full-Text
Keywords: metalorganic vapor phase epitaxy; gallium nitride; chemical adsorption; surface reconstruction; density functional theory calculations; steepest-entropy-ascent quantum thermodynamics metalorganic vapor phase epitaxy; gallium nitride; chemical adsorption; surface reconstruction; density functional theory calculations; steepest-entropy-ascent quantum thermodynamics
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Kusaba, A.; Li, G.; von Spakovsky, M.R.; Kangawa, Y.; Kakimoto, K. Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics. Materials 2017, 10, 948.

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