DFT calculations were used to investigate ammonia adsorption on GaN(0001) surface under mixed coverage composed of H adatoms, NH₂ radicals and NH₃ admolecules typical for the growth of GaN layers and crystals by MOVPE, HVPE and ammonothermal methods. The investigation elucidated role of electronic properties of the surface on the course of adsorption processes showing important role of electronic degrees of freedom in some cases. In the case of bare surface ammonia adsorption is dissociative: it leads to dissociation of ammonia and adsorption of NH₂ radicals and single H adatoms. The adsorption energy is close to 2.9 eV/molecule. For very low hydrogen coverage the ammonia adsorption follows the pattern of clean surface dissociation to NH₂ radicals and H adatoms which is caused by tendency to saturate broken Ga bonds. The increase of hydrogen coverage stabilizes ammonia molecule that is adsorbed in the molecular form at the surface with the reduction of adsorption energy to about 2 eV. This is related to tendency of GaN(0001) surface of to avoid pinning Fermi level at the surface states. In this case the adsorption of ammonia preserves its molecular structure, with only single molecular bond transformed into highly dispersive state located in the upper subband of GaN valence band. Finally for full coverage, the adsorption leads to creation of Ga-H-N bond weakly attaching the molecule with the energy. Further evolution of the system may either lead to return of the ammonia to the vapor or desorption of H₂ molecule with NH₂ radical attached to the surface. For higher content of ammonia admolecules or NH₂ radicals the pattern is changed, the adsorption affects the bonding of ammonia changing the bonding structure of the admolecule. This is related to change of the Fermi level at the surface which is shifted up into the conduction band. This change drastically reduces the bonding energy making the ammonia adsorbed admolecule unstable at the GaN(0001) surface for relatively high NH₃/NH₂ ratio. 

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29936 must be provided.

1. GaN/AlN junctions - density functional study
2. Density Functional Theory (DFT) study of GaN(0001) surface in ammonia rich conditions - influence of doping type
3. An influence of parallel electric field on the dispersion relation of graphene – a new route to Dirac logics
4. Drift-diffusion simulations of gallium nitride based heterostructures
5. Absorption and emission spectra of InN/GaN superlattice structures by DFT methods
6. Absorption and emission spectra of AlN/GaN superlattice structures by DFT methods
7. Bulk GaAs growth by Contactless Liquid Phase Electroepitaxy
8. Adsorption of gallium on GaN(0001) surface in ammonia rich conditions - Density Functional Theory (DFT) study
9. Density Functional Theory (DFT) study of hydrogen on GaN (0001) surface
10. Surface structure and diffusion of Si and C adatoms on bare SiC(0001) and SiC(0001) surfaces- density functional theory studies
11. First-principles calculations of structural and electronic properties of GaN(0001)/Ga interface
12. A density functional  theory study of the Zn, O, O₂, and H₂O adsorption on the polar ZnO(0001) and ZnO(000-1) surfaces
13. Surface morphology of InGaN layers
14. Modelling of the growth of nitrides in ammonia rich environment
15. Transport properties on nitrogen at high pressure and temperature: viscosity – MD study.
16. Adsorption processes during growth of GaN by HVPE
17. Rietveld refinement for polycrystalline indium nitride
18. Mass flow and reaction analysis of the growth of GaN layers by HVPE