Band bending and photoemission-induced surface photovoltages on clean<i>n</i>- and<i>p</i>-GaN (0001) surfaces

Long, J. P.; Bermudez, V. M.

doi:10.1103/physrevb.66.121308

Cited by 118 publications

(90 citation statements)

References 25 publications

(21 reference statements)

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“…As commented before, when the surface depleted area is larger than the NW radius no neutral region exists in the wire core, and the surface band bending is effectively reduced. Based on would imply an opposite V CPD change, namely a decrease for the p-type NW and an increase for the n-type NW [19,28], contrary to our observations. Alternatively, the shift in VCPD induced by UV illumination could be accounted for by considering the Schottky nature of the NW/HOPG contact.…”

Section: Resultscontrasting

confidence: 57%

“…Only in the absence of surface band bending the difference VCPD between the n and p sides would correspond to the built-in potential, which for large doping is expected to be of the order of the band gap. Indeed, due to the presence of surface states and the associated band bending an upward surface band bending is expected at the m-plane surface of the n-type side [18], while for p-type GaN the band bending is expected to be downwards, as shown by Long et al for c-plane GaN [19]. As a result, the measured V CPD gives a lower limit to the junction built-in potential.…”

Section: Resultsmentioning

confidence: 87%

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Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

et al. 2016

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Making use of Kelvin probe force microscopy, in dark and under ultraviolet illumination, we study the characteristics of p-n junctions formed along the axis of self-organized GaN nanowires (NWs).We map the contact potential difference of the single NW p-n junctions to locate the space charge region and directly measure the depletion width and the junction voltage. Simulations indicate a shrinkage of the built-in potential for NWs with small diameter due to surface band bending, in qualitative agreement with the measurements. The photovoltage of the NW/substrate contact is studied by analysing the response of NW segments with p-and n-type doping under illumination. Our results show that the shifts of the Fermi levels, and not the changes in surface band bending, are the most important effects under above band-gap illumination. The quantitative electrical information obtained here is important for the use of NW p-n junctions as photovoltaic or rectifying devices at the nanoscale, and is especially relevant since the technique does not require the formation of ohmic contacts to the NW junction.2

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Section: Resultscontrasting

confidence: 57%

Section: Resultsmentioning

confidence: 87%

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

et al. 2016

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“…2,[16][17][18] Band dispersion has also been investigated using photoemission. [19][20][21][22][23][24][25] Long et al 16 used photoelectron (PES) and X-ray photoemission spectroscopy (XPS) on the clean GaN(0001) surface. In the limit of low temperature and low doping concentration, E F −E v was measured to be about 2.7 eV on the surface of n-type GaN, and about 1.3 eV on the surface of p-type GaN.…”

Section: Survey Of Experimental Resultsmentioning

confidence: 99%

Microscopic origins of surface states on nitride surfaces

Walle

Segev

2007

Journal of Applied Physics

264

208

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We report a systematic and comprehensive computational study of the electronic structure of GaN and InN surfaces in various orientations, including the polar c plane as well as the nonpolar a and m planes. Surface band structures and density-of-states plots show the energetic position of surface states, and by correlating the electronic structure with atomistic information we are able to identify the microscopic origins of each of these states. Fermi-level pinning positions are identified, depending on surface stoichiometry and surface polarity. For polar InN we find that all the surface states are located above the conduction-band minimum, and explain the source of the intrinsic electron accumulation that has been universally observed on InN surfaces.

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“…The spatial distribution of the SPV-induced charge carriers in the band-bending potential opposes the original charge distribution that gave rise to the band bending. In this way, these photoinduced charges cancel the original electrostatic potential and thus lead to a decrease in the band bending [46][47][48][49][50][51]. Insight into the delicate synergy of SPV effects and photostimulated desorption of foreign species from the sample surface will be given in Sec.…”

Section: A Bi 2 Sementioning

confidence: 99%

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

et al. 2015

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Topological insulators are a novel materials platform with high applications potential in fields ranging from spintronics to quantum computation. In the ongoing scientific effort to demonstrate controlled manipulation of their electronic structure by external means, i.e., the provision of knobs with which to tune properties, stoichiometric variation and surface decoration are two effective approaches that have been followed. In angleresolved photoelectron spectroscopy (ARPES) experiments, both approaches are seen to lead to electronic band-structure changes. Most importantly, such approaches result in variations of the energy position of bulk and surface-related features and the creation of two-dimensional electron gases. The data presented here demonstrate that a third manipulation handle is accessible by utilizing the amount of super-band-gap light a topological insulator surface has been exposed to under typical ARPES experimental conditions. Our results show that this third knob acts on an equal footing with stoichiometry and surface decoration as a modifier of the electronic band structure, and that it is in continuous and direct competition with the latter. The data clearly point towards surface photovoltage and photoinduced desorption as the physical phenomena behind modifications of the electronic band structure under exposure to high-flux photons. We show that the interplay of these phenomena can minimize and even eliminate the adsorbate-related surface band bending on typical binary, ternary, and quaternary Bi-based topological insulators. Including the influence of the sample temperature, these data set up a detailed framework for the external control of the electronic band structure in topological insulator compounds in an ARPES setting. Four external knobs are available: bulk stoichiometry, surface decoration, temperature, and photon exposure. These knobs can be used in conjunction to fine tune the band energies near the surface and consequently influence the topological properties of the relevant electronic states.

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Band bending and photoemission-induced surface photovoltages on cleann- andp-GaN (0001) surfaces

Cited by 118 publications

References 25 publications

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

Microscopic origins of surface states on nitride surfaces

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

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