Abstract

It is demonstrated how quantum effects play determining role in nitrogen adatom diffusion via specification of several different factors. The first is related to the bonding both in the initial and activated complex states. It is shown that wurtzite gallium nitride is bonded differently from standard semiconductors, by two separate valence band subbands. The upper is by gallium 4sp3 hybridized orbitals and nitrogen resonant 2p states, the lower by gallium 3d and nitrogen 2s orbitals. This could change of the energy of the quantum states in both the initial and the saddle point state. In addition the diffusion energy barrier may be changed due to the redistribution of electrons between the quantum states, both standard and resonant, via quantum statistics governed by the Fermi energy level. These effects were studied in the case of nitrogen diffusion over clean and gallium covered Ga-terminated GaN(0001) surface. For the fractional coverage the density functional theory (DFT) calculations show that at the saddle point configuration the redistribution of electrons between different quantum states may affect the surface diffusion barrier significantly. The other quantum influence occurs via the change of the minimal energy configuration. Under fractional Ga coverage of GaN(0001) surface the nitrogen diffusion energy barrier proceeds from the resonant states governed energy minimal H₃ site across the saddle point in the bridge configuration. At this path the barrier is affected the electron redistribution between surface quantum states both in the initial and the saddle point. In the case of the full GaN coverage the diffusion path is from on-top N adatom configuration via H₃ site that corresponds to maximal energy. Therefore the diffusion barrier is ∆Ebar= 1.18 eV for clean and ∆Ebar= 0.92 eV for (1/6)ML to finally ∆Ebar= 1.23 eV for full Ga coverage. Thus the overall barrier is reduced to ∆Ebar= 0.92 eV due to quantum statistics effects. The identified stable N on-top configuration for the full coverage is essential for atomic mechanism of GaN growth in Ga-rich regime.

Abstract

It is demonstrated how quantum effects play determining role in nitrogen adatom diffusion via specification of several different factors. The first is related to the bonding both in the initial and activated complex states. It is shown that wurtzite gallium nitride is bonded differently from standard semiconductors, by two separate valence band subbands. The upper is by gallium 4sp3 hybridized orbitals and nitrogen resonant 2p states, the lower by gallium 3d and nitrogen 2s orbitals. This could change of the energy of the quantum states in both the initial and the saddle point state. In addition the diffusion energy barrier may be changed due to the redistribution of electrons between the quantum states, both standard and resonant, via quantum statistics governed by the Fermi energy level. These effects were studied in the case of nitrogen diffusion over clean and gallium covered Ga-terminated GaN(0001) surface. For the fractional coverage the density functional theory (DFT) calculations show that at the saddle point configuration the redistribution of electrons between different quantum states may affect the surface diffusion barrier significantly. The other quantum influence occurs via the change of the minimal energy configuration. Under fractional Ga coverage of GaN(0001) surface the nitrogen diffusion energy barrier proceeds from the resonant states governed energy minimal H₃ site across the saddle point in the bridge configuration. At this path the barrier is affected the electron redistribution between surface quantum states both in the initial and the saddle point. In the case of the full GaN coverage the diffusion path is from on-top N adatom configuration via H₃ site that corresponds to maximal energy. Therefore the diffusion barrier is ∆Ebar= 1.18 eV for clean and ∆Ebar= 0.92 eV for (1/6)ML to finally ∆Ebar= 1.23 eV for full Ga coverage. Thus the overall barrier is reduced to ∆Ebar= 0.92 eV due to quantum statistics effects. The identified stable N on-top configuration for the full coverage is essential for atomic mechanism of GaN growth in Ga-rich regime.

Abstract

It is demonstrated how quantum effects play determining role in nitrogen adatom diffusion via specification of several different factors. The first is related to the bonding both in the initial and activated complex states. It is shown that wurtzite gallium nitride is bonded differently from standard semiconductors, by two separate valence band subbands. The upper is by gallium 4sp3 hybridized orbitals and nitrogen resonant 2p states, the lower by gallium 3d and nitrogen 2s orbitals. This could change of the energy of the quantum states in both the initial and the saddle point state. In addition the diffusion energy barrier may be changed due to the redistribution of electrons between the quantum states, both standard and resonant, via quantum statistics governed by the Fermi energy level. These effects were studied in the case of nitrogen diffusion over clean and gallium covered Ga-terminated GaN(0001) surface. For the fractional coverage the density functional theory (DFT) calculations show that at the saddle point configuration the redistribution of electrons between different quantum states may affect the surface diffusion barrier significantly. The other quantum influence occurs via the change of the minimal energy configuration. Under fractional Ga coverage of GaN(0001) surface the nitrogen diffusion energy barrier proceeds from the resonant states governed energy minimal H₃ site across the saddle point in the bridge configuration. At this path the barrier is affected the electron redistribution between surface quantum states both in the initial and the saddle point. In the case of the full GaN coverage the diffusion path is from on-top N adatom configuration via H₃ site that corresponds to maximal energy. Therefore the diffusion barrier is ∆Ebar= 1.18 eV for clean and ∆Ebar= 0.92 eV for (1/6)ML to finally ∆Ebar= 1.23 eV for full Ga coverage. Thus the overall barrier is reduced to ∆Ebar= 0.92 eV due to quantum statistics effects. The identified stable N on-top configuration for the full coverage is essential for atomic mechanism of GaN growth in Ga-rich regime.

Abstract

It is demonstrated how quantum effects play determining role in nitrogen adatom diffusion via specification of several different factors. The first is related to the bonding both in the initial and activated complex states. It is shown that wurtzite gallium nitride is bonded differently from standard semiconductors, by two separate valence band subbands. The upper is by gallium 4sp3 hybridized orbitals and nitrogen resonant 2p states, the lower by gallium 3d and nitrogen 2s orbitals. This could change of the energy of the quantum states in both the initial and the saddle point state. In addition the diffusion energy barrier may be changed due to the redistribution of electrons between the quantum states, both standard and resonant, via quantum statistics governed by the Fermi energy level. These effects were studied in the case of nitrogen diffusion over clean and gallium covered Ga-terminated GaN(0001) surface. For the fractional coverage the density functional theory (DFT) calculations show that at the saddle point configuration the redistribution of electrons between different quantum states may affect the surface diffusion barrier significantly. The other quantum influence occurs via the change of the minimal energy configuration. Under fractional Ga coverage of GaN(0001) surface the nitrogen diffusion energy barrier proceeds from the resonant states governed energy minimal H₃ site across the saddle point in the bridge configuration. At this path the barrier is affected the electron redistribution between surface quantum states both in the initial and the saddle point. In the case of the full GaN coverage the diffusion path is from on-top N adatom configuration via H₃ site that corresponds to maximal energy. Therefore the diffusion barrier is ∆Ebar= 1.18 eV for clean and ∆Ebar= 0.92 eV for (1/6)ML to finally ∆Ebar= 1.23 eV for full Ga coverage. Thus the overall barrier is reduced to ∆Ebar= 0.92 eV due to quantum statistics effects. The identified stable N on-top configuration for the full coverage is essential for atomic mechanism of GaN growth in Ga-rich regime.