Institute of High Pressure Physics

In the recent paper by  Paweł Strak, Cyprian Sobczak and Stanislaw Krukowski „Quantum statistics effects in surface diffusion: application to diffusion of nitrogen adatoms over GaN(0001) surface” published in Physical Chemistry Chemical Physics, 2025, 27, 23996-24016, authors from our Institute have demonstrated that quantum statistics effects play an important role in nitrogen adatom diffusion over partially Ga-covered GaN(0001) surfaces. This is partially related to the bonding in both the initial and activated complex states. Additionally, the diffusion energy barrier may be changed owing to the quantum statistics of electrons governed by the Fermi energy, as shown in the case of nitrogen diffusion over a clean and gallium-covered Ga-terminated GaN(0001) surface.

Energies of the quantum states of the nitrogen adatom and next nearest neighboring (nnn) gallium atoms states in the (2√3x2√3) slab representing clean GaN(0001) surface with single N adatom located in H3 site. The indices 1, 2 and 3 correspond to the nearest neighboring Ga atoms (tetrahedron) located in the basis of the tetrahedron. The panels represents, from the left: energy of the quantum states in the momentum space, projected density of states (PDOS) of the N and Ga atoms, and the right two panel - Crystal Orbital Hamilton Population (COHP).

It is shown that wurtzite gallium nitride is bonded differently from standard semiconductors having two separate valence subbands: upper by gallium 4sp³ hybridized orbitals and nitrogen resonant 2p states, and lower by gallium 3d and nitrogen 2s orbitals. Second, the diffusion energy barrier may be changed owing to the quantum statistics of electrons governed by the Fermi energy, as shown in the case of nitrogen diffusion over a clean and gallium-covered Ga-terminated GaN(0001) surface. Under fractional Ga coverage of the GaN(0001) surface, the nitrogen diffusion energy barrier is at the saddle point. The barrier affects the electron redistribution between the surface quantum states at both the initial and saddle points. In the case of full GaN coverage, the diffusion path is from the top N adatom configuration to the H3 site, which corresponds to the maximal energy. Therefore the diffusion barrier changes from ΔEbar = 1.18 eV for clean to ΔEbar = 0.92 eV for (1/6) ML and finally to ΔEbar = 1.23 eV for full Ga coverage. Thus, the overall barrier was ΔEbar = 0.92 eV. The identified stable N-on-top configuration for Ga coverage is essential for the GaN growth mechanism.