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.
Highlights
GaN and related alloys are well-known materials for UV/blue light-emitting diodes (LEDs) and laser diodes (LDs) [1,2,3]
Unlike the case of molecular beam epitaxy (MBE), the in-situ observation of reconstructed structures during metalorganic vapor phase epitaxy (MOVPE) is difficult because electron diffraction methods such as RHEED are not available at non-vacuum MOVPE pressures
density functional theory (DFT) can be coupled to steepest-entropy-ascent quantum thermodynamics (SEAQT), which is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes even those far from equilibrium
Summary
GaN and related alloys are well-known materials for UV/blue light-emitting diodes (LEDs) and laser diodes (LDs) [1,2,3]. DFT can be coupled to steepest-entropy-ascent quantum thermodynamics (SEAQT), which is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes even those far from equilibrium This framework has been developed and applied to both non-reacting and reacting systems at multiple spatial and temporal scales and validated via comparisons with experiments [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41].
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