Confirmation of intrinsic electron gap states at nonpolar GaN(1-100) surfaces combining photoelectron and surface optical spectroscopy

Himmerlich, Marcel; Eisenhardt, Anja; Shokhovets, S.; Krischok, S.; Räthel, J.; Speiser, E.; Neumann, M.; Navarro-Quezada, A.; Esser, N.

doi:10.1063/1.4873376

Cited by 31 publications

(32 citation statements)

References 26 publications

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“…[36]. due to the presence of intra-gap states (S N and S Ga ) in the surface band structure, in agreement with recent experimental results [41]. At the GaN(1 01 0) surface, the presence of one Ga and N atom per unit cell leads to one empty and one filled dangling bond state, respectively.…”

Section: Resultssupporting

confidence: 83%

“…The empty Ga dangling bond (S Ga ) has a stronger dispersion, around 1.8 eV, with the minimum and maximum at the -point and X-point, respectively. Recent photoelectron spectroscopy, reflection anisotropy spectroscopy, and STM experiments at the GaN(1 01 0) surface suggest no electronic surface states in the fundamental band gap [38,41,42], as was observed in the present paper.…”

Section: Resultssupporting

confidence: 70%

“…3(b)). The dispersion of this dangling bond state (S N ) is around ∼0.5 eV, which is close to the recent the experimental photoemission value, which is ∼0.4 eV lower at the X-point compared to the -point [41]. The empty Ga dangling bond (S Ga ) has a stronger dispersion, around 1.8 eV, with the minimum and maximum at the -point and X-point, respectively.…”

Section: Resultssupporting

confidence: 66%

See 2 more Smart Citations

A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

González‐Hernández

González-García

Barragan-Yani

et al. 2014

Applied Surface Science

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Section: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 70%

Section: Resultssupporting

confidence: 66%

See 1 more Smart Citation

A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

González‐Hernández

González-García

Barragan-Yani

et al. 2014

Applied Surface Science

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“…[23,[36][37][38] Nonetheless, the former region has not been observed or predicted so far. The latter region of the Fermi level localization is expected to extend in the direction of the conduction band since CER measurements in air ambient allowed to observe the Fermi level position at ≈0.4 eV below CB that was observed earlier.…”

Section: Wwwadvmatinterfacesdementioning

confidence: 93%

Depletion Layer Built‐In Field at (1−100), (0001), and (000−1) GaN/Water Junction and Its Role in Semiconductor Nanowire Water Splitting

Stokowski

Janicki

Serafińczuk

et al. 2019

Adv Materials Inter

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IntroductionFollowing the discovery of semiconductor-based photoelectrolysis by Fujishima and Honda, [1] a considerable attention has been given to this phenomenon as a very promising for clean, sustainable, and storable fuel generation. [2][3][4][5][6] An important aspect of consideration is exploring various kinds of materials and structures to optimize the water-splitting efficiency. The main requirement for the electrode material is a suitable bandgap, which not only allows harvesting the sunlight energyThe nature of specific GaN plane/water interfaces under external bias and illumination can influence photoelectrolysis efficiency using GaN nanowires. Studies of Ga-polar, N-polar, and m-plane GaN interfaces with deionized water allow determining differences between surfaces corresponding to different nanowire facets. They are investigated under external bias conditions to reveal the profile of Fermi level localization through analysis of Franz-Keldysh oscillations using electrolyte electroreflectance (EER) technique in a specially designed measurement chamber. Calculation of the potential barrier height is also possible. EER study shows differences between surface densities of states (SDOS) at distinct GaN planes. One broad SDOS is identified near the conduction band in case of ±c-plane and related to Ga adatom reconstruction and β-Ga 2 O 3 presence at the GaN electrode. Two narrow SDOS singularities are found at the m-plane one of which is localized near the middle of the bandgap and allows to generate approximately two times higher surface potential barrier than in case of polar surfaces at zero-bias conditions. This suggests that n-type GaN nanowires can enhance carrier separation at sidewalls and refine the oxygen evolution rate. Additionally, a voltage-controlled hysteresis loop of Fermi level localization is detected at the Ga-face GaN/water interface.but also is sufficient to overcome overpotentials necessary to split water molecules. One of the most promising materials in this context is gallium nitride, which has been reported useful both as a solid electrode [7] and in a form of nanowire arrays. [8,9] Due to the polar character of the wurtzite crystal structure of GaN, the nature of particular planes in nanowires can differ and result in a change of performance in photoelectrolysis. Especially, the built-in electric field emerging at the surface of GaN brought in a contact with water can have tremendous consequences on photogenerated carriers' separation and their transfer to the surface, where the hydrogen-and oxygen-evolution reactions are driven. The above-mentioned fields and band bending [10] are controlled by the Fermi level pinning at the gallium nitride surface states which are dependent upon the crystal plane choice. [11] In case of wurtzite crystal-based nanowires the most interesting are (0001) c-plane and (1−100) m-plane which usually correspond to the top and side walls of these structures, respectively.Studies of the Fermi level position at semiconductor/water interface can be challeng...

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“…On the GaN surface, we include an empty S Ga surface state within the band gap as found previously. 28,29,32,33 The surface state was modelled as a Gaussian density of states distribution with a FWHM of 0.3 eV and a peak energy 0.59 eV below the conduction band edge. We assume that the occupation of the surface state is in thermal equilibrium with the Fermi-level.…”

Section: à3mentioning

confidence: 99%

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

Hsiao

Schnedler

Portz

et al. 2017

Journal of Applied Physics

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We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

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Confirmation of intrinsic electron gap states at nonpolar GaN(1-100) surfaces combining photoelectron and surface optical spectroscopy

Cited by 31 publications

References 26 publications

A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

Depletion Layer Built‐In Field at (1−100), (0001), and (000−1) GaN/Water Junction and Its Role in Semiconductor Nanowire Water Splitting

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

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