Electronic structure of GaN and Ga investigated by soft x-ray spectroscopy and first-principles methods

Magnuson, Martin; Mattesini, Maurizio; Höglund, Carina; Birch, Jens; Hultman, Lars

doi:10.1103/physrevb.81.085125

Cited by 81 publications

(75 citation statements)

References 44 publications

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“…48,49 In accordance to the angle resolved photoelectron spectroscopy (ARPES) results 48 and the DFT simulations, 49 the valence band consists of the two subbands separated by a 5 eV wide gap. The upper subband is composed of Ga 4s -4p and N 2p states.…”

Section: B Fermi Level Not Pinned At Gan(0001) Surface -Electron Coumentioning

confidence: 63%

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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: B Fermi Level Not Pinned At Gan(0001) Surface -Electron Coumentioning

confidence: 63%

“…The upper subband is composed of Ga 4s -4p and N 2p states. 48 Thus gallium is sp 3 -hybridized in bonding and nitrogen is not. The lower subband is composed of Ga 3d and N 2s states.…”

Section: B Fermi Level Not Pinned At Gan(0001) Surface -Electron Coumentioning

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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“…2(b): U O:2p = 7.4 eV, and U Zn:3d = 8.5 eV. Using the same approach we deduce the values of U N:2p and U Ga:3d which are equal to 4.7 eV and 10.0 eV [19], respectively.…”

Section: Resultsmentioning

confidence: 93%

“…The calculation details is briefly described in the following [24]. Firstly a slab model with the non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) surface orientation is constructed, including nine ZnO (or GaN) layers. Then we calculate the averaged electrostatic potential difference between the inside of the slab and vacuum region.…”

Section: Resultsmentioning

confidence: 99%

First-principles simulations of two dimensional electron gas near the interface of ZnO/GaN (0001) superlattice

Zhu

2015

Physics Letters A

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“…The Hubbard correction improved the description of the bandgap of GaN (ZnO), going from 1.7 (0.8) eV to 2.2 (1.6) eV. This correction still underestimates the bandgap of GaN (ZnO) as compared to the experimental value of 3.5 (3.4) eV [21,22]. We then implemented the correction in the 4f states of the RE impurities within the same methodology, in order to get an appropriate description of the highly correlated 4f-related electronic states.…”

mentioning

confidence: 99%

Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

Caroena

Machado

Justo

et al. 2013

Applied Physics Letters

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The electronic properties of lanthanide (from Eu to Tm) impurities in wurtzite gallium nitride and zinc oxide were investigated by first principles calculations, using an all electron methodology plus a Hubbard potential correction. The results indicated that the 4f-related energy levels remain outside the bandgap in both materials, in good agreement with a recent phenomenological model, based on experimental data. Additionally, zinc oxide doped with lanthanide impurities became an n-type material, showing a coupling between the 4f-related spin polarized states and the carriers.This coupling may generate spin polarized currents, which could lead to applications in spintronic devices. [2,3] devices. Rare earth lanthanide atoms exhibit partially filled 4f shells, and intra-4f electric dipole transitions are forbidden for the free ions. On the other hand, the respective transition probabilities increase considerably when the ions are placed in a crystal field, that splits the 4f-related energy levels, modifying the dipole selection rules and leading to luminescent centers [4].Although theoretical modeling has been used to investigate the properties of RE-related materials [5,6], several methodological challenges have hindered an appropriate description of the 4f-related states in crystalline environments, such as RE impurities in semiconductors.It is well documented that the density functional theory generally fails in describing highly correlated systems, such as the interactions in 4f-related electronic states. Such limitations could in part be overcome with the introduction of an on-site Hubbard U potential correction [7][8][9]. One of the major outcomes of this correction is a better description of the energy splitting between occupied and unoccupied 4f-related electronic levels. We have recently shown that this procedure provides a good description of the electronic structure of metallic RE crystals [10], when compared to available experimental data [11]. Here, we show that the same procedure is also appropriate to describe the trends on the 4f-related energy levels of RE impurities (from Eu to Tm), with respect to the bandgap, in wurtzite gallium nitride and zinc oxide crystals. The results were discussed in the context of a recent phenomenological model to determine the energy positions of 4f-related electronic systems in crystalline environments [12]. Our results also indicate that doping ZnO with lanthanide impurities leads to a ntype material, with a magnetic coupling between the 4f-related states and the carriers.This suggests that such systems could generate spin polarized carrier currents, allowing to envision potential applications in spintronic devices.In RE lanthanide atoms, the 4f states play a minor role on bonding, staying in an atomiclike configuration. Therefore, those atoms bind to their neighboring ones through their outer (5d, 6s, and 6p) atomic valence states [11]. Earlier theoretical investigations generally considered the 4f electrons as core states, with constrained occupations ...

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Electronic structure of GaN and Ga investigated by soft x-ray spectroscopy and first-principles methods

Cited by 81 publications

References 44 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 simulations of two dimensional electron gas near the interface of ZnO/GaN (0001) superlattice

Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

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