Abstract
We outline a molecular mechanics model for the interaction of gallium and nitride ions ranging from small complexes to nanoparticles and bulk crystals. While the current GaN force fields allow the modelling of either bulk crystals or single ions dispersed in solution, our model covers both and hence paves the way to describing aggregate formation and crystal growth processes from molecular simulations. The key to this is the use of formal +3 and −3 charges on the gallium and nitride ions, whilst accounting for the charge transfer in GaN crystals by means of additional potential energy terms. The latter are fitted against experimental data of GaN in the wurtzite structure and benchmarked for the zinc-blende and rock-salt polymorphs. Comparison to quantum chemical references and experiment shows reasonable agreement of structures and formation energy of [GaN]n aggregates, elastic properties of the bulk crystal, the transition pressure of the wurtzite to rock-salt transformation and intrinsic point defects. Furthermore, we demonstrate force field transferability towards the modelling of GaN nanoparticles from simulated annealing runs.
Highlights
Gallium nitride is a direct band-gap semiconductor with appealing properties thanks to its wide band-gap (~3.2 eV) [1], high thermal conductivity (~2.3 W−1) [2] and favorable electron mobility (~1500 cm2 V−1 s−1) [2]
We outline a molecular mechanics model for the interaction of gallium and nitride ions ranging from small complexes to nanoparticles and bulk crystals
While the current GaN force fields allow the modelling of either bulk crystals or single ions dispersed in solution, our model covers both and paves the way to describing aggregate formation and crystal growth processes from molecular simulations
Summary
Gallium nitride is a direct band-gap semiconductor with appealing properties thanks to its wide band-gap (~3.2 eV) [1], high thermal conductivity (~2.3 W (cm K)−1) [2] and favorable electron mobility (~1500 cm V−1 s−1) [2]. Crystals of GaN permit broad applications, ranging from (opto-) electronic devices to gas sensors. This is hampered by the ongoing challenge of producing high-quality single crystals— which inspired considerable research efforts from both experiment and theory. Using the buffer-layer technique and developing the idea of double heterostructures, Akasaki, Amano and Nakamura [5, 6] demonstrated the first blue light-emitting diode using GaN and its ternary alloy with indium, InxGa1−xN [7]. This important contribution led to the Nobel Prize in Physics in 2014. GaN has high melting temperature and chemical resistance
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