Modelling the growth of nitrides in ammonia‐rich environment

Abstract

Key words gallium nitride, hydrogen vapor phase epitaxy, metal organic vapor phase epitaxy, density functional theory. PACS 61.50.Ah, 81.10.Aj Surface properties and the principal processes at the growth of gallium nitride on GaN (0001) face in ammonia-based are modeled using DFT (density functional theory -SIESTA code) ab initio calculations and 2-d diffusion analysis. The GaN growth methods are: ammonia-source MBE, MOVPE, and also HVPE. The adiabatic trajectories, calculated for hydrogen-rich and hydrogen-free state of the GaN(0001) surface, include the adsorption of NH 3 , GaCl and HCl molecules and the desorption of Ga atoms. The adsorption of ammonia and GaCl has no energy barrier. Thus, in contrast to the results concerning Plasma-Assisted Molecular Beam Epitaxy (PA MBE), proving that the GaN(0001) surface remains in metal-rich state, these results indicate that, in the ammonia-rich environment, typical for HVPE and MOVP growth, the GaN(0001) surface remains in the nitrogen-rich state. In the case of HCl adsorption, the energy barrier depends on the surface coverage, and could reach 2.0 eV. The direct desorption of single Ga atom has the energy barrier, close to 7 eV. This indicates that Ga surface diffusion (growth controlling process) length is very large, leading to strong interaction of the step kinetics and the diffusion on the terraces. This interaction leads to double-step intertwined structures both in the case of dislocation-mediated spiral growth and in the step flow growth mode. These morphologies, proposed by the geometric arguments, are observed in the atomic force microscopy (AFM) scans of the GaN(0001) surface. Additionally we have compared the interaction energy of two hydrogen atoms obtained in the DFT SIESTA and the high precision Gaussian in coupled cluster singles, double and perturbation triples CCSD(T) approximation. Both approaches yielded virtually identical interaction energy confirming the validity of DFT analysis of ammonia-rich growth of GaN.

Emergence of regular meandered step structure in simulated growth of GaN(0001) surface

“…Similar meandered structures have been lately observed at GaN(0001)surface [14,15]. In addition, in Monte Carlo simulations such behavior was observed [18].…”

“…Meandering often evolves into a regular finger-like structures at the surface. Such regular structures are quite often observed GaN surface morphologies [14,15]. Similar structures are also created at Si(111) surface [17].…”

“…It was shown that the characteristic anisotropy of step dynamics can be modeled by using four-body interaction. It was also shown that in addition to step pairing of ½1010 steps, step meandering can be obtained for large system sizes, which is observed in real crystal growth experiments [14,15]. As it was lately discussed in Ref.…”

“…Steps can form bunches, but also bend creating characteristic meanders. Instability phenomena, denoted as step meandering, were observed during the growth of different crystal types [8][9][10][11][12][13][14][15]. The experimental data include step meandering in various systems, both metallic and semiconductor.…”

Review: GaN growth by ammonia based methods – density functional theory study

“…The energy barrier for the transition to chemisorbed state is lower than 10 meV, i.e. is of order of the precision of the calculations [60].…”