<b><i>Ab initio</i></b>calculation of the stoichiometry and structure of the (0001) surfaces of GaN and AlN

Fritsch, Jürgen; Sankey, Otto F.; Schmidt, Kevin; Page, J. B.

doi:10.1103/physrevb.57.15360

Cited by 97 publications

(85 citation statements)

References 53 publications

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“…The NH 2 radical was bound to gallium and the H atom to gallium and nitrogen broken bonds. 16 The reconstruction was not confirmed by any other calculations. The adsorption energy barrier was found to be of order of 0.5 eV.…”

Section: Introductionmentioning

confidence: 82%

“…12,13 These results were confirmed by the DFT determination of the stable structures of polar and nonpolar GaN(0001) surfaces by Ito et al 14 The reaction of ammonia with a bare and H-covered GaN(0001) surface was investigated by several groups by ab initio modeling. [15][16][17][18][19][20] Fritsch et al simulated several configurations of GaN(0001) surface, showing that ammonia adsorption is dissociative to H and a NH 2 radical and transformation of the GaN(0001) flat surface into a p(2 × 2) vacancy reconstruction. The NH 2 radical was bound to gallium and the H atom to gallium and nitrogen broken bonds.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

Kempisty

Krukowski

2014

AIP Advances

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Adsorption of ammonia at NH 3 /NH 2 /H covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH 3 /NH 2 /H covered GaN(0001) surface was divided into zones differently pinned Fermi level: at Ga broken bond state for dominantly bare surface (region I), at VBM for NH 2 and H covered (region II), and at CBM for NH 3 covered surface (region III). The extensive ab intio calculations show validity of electron counting rule (ECR) for all mixed coverage, for bordering these three regions. The adsorption was analyzed using newly identified dependence of the adsorption energy on the charge transfer at the surface. For region I and II ammonia adsorb dissociatively, disintegrating into H adatom and HN 2 radical for large fraction of vacant sites while for high coverage the ammonia adsorption is molecular. The dissociative adsorption energy strongly depends on the Fermi level at the surface (pinned) and in the bulk (unpinned) while the molecular adsorption energy is determined by bonding to surface only, in accordance to the recently published theory. The molecular adsorption is determined by the energy of covalent bonding to the surface. Ammonia adsorption in region III (Fermi level pinned at CBM) leads to unstable configuration both molecular and dissociative which is explained by the fact that Ga-broken bond sites are doubly occupied by electrons. The adsorbing ammonia brings 8 electrons to the surface, necessitating transfer of the electrons from Ga-broken bond state to Fermi level, energetically costly process.Adsorption of ammonia at H-covered site leads to creation of NH 2 radical at the surface and escape of H 2 molecule. The process energy is close to 0.12 eV, thus not large, but the inverse process is not possible due to escape of the hydrogen molecule.

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Section: Introductionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

Kempisty

Krukowski

2014

AIP Advances

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“…Since we are particularly interested in consequences for growth, it is essential to take finite temperature effects into account, requiring the calculation of free energies. This distinguishes our approach from previous work in which only zerotemperature energies were calculated, and then only for a small number of structures [2][3][4]. We will show that the energetic and structural features of the surface reconstructions dramatically depend on temperature (T) and pressure (p).…”

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confidence: 86%

First-Principles Surface Phase Diagram for Hydrogen on GaN Surfaces

2002

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We discuss the derivation and interpretation of a generalized surface phase diagram, based on firstprinciples density-functional calculations. Applying the approach to hydrogenated GaN surfaces, we find that the Gibbs free energies of relevant reconstructions strongly depend on temperature and pressure. Choosing chemical potentials as variables results in a phase diagram that provides immediate insight into the relative stability of different structures. A comparison with recent experiments illustrates the power of the approach for interpreting and predicting energetic and structural properties of surfaces under realistic growth conditions. DOI: 10.1103/PhysRevLett.88.066103 PACS numbers: 68.35. -p, 68.43. -h, 81.10. -h A detailed understanding of semiconductor surface reconstructions is essential for controlling growth and materials properties. In the case of GaN, where materials quality is still limiting device progress, the investigations until now have focused on reconstructions of bare GaN surfaces [1]. The present study focuses on the role of hydrogen (H), which is important because H is abundantly present in the most commonly used growth techniques for nitride semiconductors, including metal-organic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxy (HVPE), and molecular-beam epitaxy (MBE) when NH 3 is used as the nitrogen source.We have therefore performed detailed investigations of H interactions with GaN surfaces based on state-of-the-art pseudopotential-density-functional calculations. We focus on the technologically most relevant GaN(0001) surface, which is the polarity observed during MOCVD of GaN on sapphire as well as MBE on Si-face SiC. Since we are particularly interested in consequences for growth, it is essential to take finite temperature effects into account, requiring the calculation of free energies. This distinguishes our approach from previous work in which only zerotemperature energies were calculated, and then only for a small number of structures [2][3][4]. We will show that the energetic and structural features of the surface reconstructions dramatically depend on temperature (T) and pressure (p).In thermochemistry, the Gibbs free energy G is usually expressed as a function of T and partial pressures. An alternative approach is to use chemical potentials m as variables and to express G as a function of p, T, and all independent m's. For the system at hand, the Gibbs' Phase Rule produces four degrees of freedom, resulting in a four-dimensional phase space that is difficult to analyze or visualize. Our detailed analysis will show that the explicit dependence on p and T is small and can be neglected. The surface energy can then be expressed solely as a function of the chemical potentials m Ga and m H , while the p and T dependence is implicit. The advantage of this methodology is its physically intuitive character. Comparison with experiment requires only that the chemical potentials be evaluated as a function of T and partial pressures. The power of this approach will b...

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“…The stable reconstructed surface structure is (2 × 2) for AlN [4]. However, since no superstructures were observed for the surfaces during the AlN growth, we assumed to adopt the (1 × 1) surface unit shown in Fig.…”

Section: Models and Methods Of Calculationsmentioning

confidence: 99%

Ultrathin metal layers to convert surface polarity of nitride semiconductors

Nakayama

Mikami

2005

Physica Status Solidi (b)

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The possibility of the surface-polarity conversion of AlN upon the deposition of ultrathin Al metal layers is investigated by the first-principles theoretical calculations. It is shown that, reflecting the crystal structures of underlying layers and the binding-energy difference between Al -N and Al -Al bonds, the surface-polarity conversion from N-face to Al-face polarity becomes possible only when the deposited Al metal layers have wurtzite structure and two-monolayer thickness.

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Ab initiocalculation of the stoichiometry and structure of the (0001) surfaces of GaN and AlN

Cited by 97 publications

References 53 publications

Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

First-Principles Surface Phase Diagram for Hydrogen on GaN Surfaces

Ultrathin metal layers to convert surface polarity of nitride semiconductors

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