Direct Measurements of Fermi Level Pinning at the Surface of Intrinsically n-Type InGaAs Nanowires

Speckbacher, Maximilian; Treu, Julian; Whittles, Thomas J.; Linhart, W. M.; Xu, Xiaomo; Saller, Kai; Dhanak, Vinod R.; Abstreiter, G.; Finley, Jonathan J.; Veal, T. D.; Koblmüller, Gregor

doi:10.1021/acs.nanolett.6b02061

Cited by 66 publications

(49 citation statements)

References 45 publications

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“…The increase in the surface states density leads to a shift of the Fermi level towards the neutrality level where it is pinned in both intrinsic and n-doped nanowires as soon as the surface states density exceeds 10 12 cm −2 . The latter is in agreement with the recent direct measurement of the Fermi level position at the surface of intrinsic InGaAs nanowires exposed to air 41 . What is more important, that Fig.…”

Section: Theoretical Modelsupporting

confidence: 92%

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Features of electron gas in InAs nanowires imposed by interplay between nanowire geometry, doping and surface states

Degtyarev¹,

Khazanova²,

Demarina

2017

Sci Rep

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We present a study of electron gas properties in InAs nanowires determined by interaction between nanowire geometry, doping and surface states. The electron gas density and space distribution are calculated via self-consistent solution of coupled Schroedinger and Poisson equations in the nanowires with a hexagonal cross-section. We show that the density of surface states and the nanowire width define the spatial distribution of the electrons. Three configurations can be distinguished, namely the electrons are localized in the center of the wire, or they are arranged in a uniform tubular distribution, or finally in a tubular distribution with additional electron accumulation at the corners of the nanowire. The latter one is dominating for most experimentally obtained nanowires. N-type doping partly suppresses electron accumulation at the nanowire corners. The electron density calculated for both, various nanowire widths and different positions of the Fermi level at the nanowire surface, is compared with the experimental data for intrinsic InAs nanowires. Suitable agreement is obtained by assuming a Fermi level pinning at 60 to 100 meV above the conduction band edge, leading to a tubular electron distribution with accumulation along the corners of the nanowire.Electron and hole gas in semiconductor nanowires of the sizes compared to the de Broglie wavelength is a fascinating object since its properties are determined by quantum-mechanical effects. Moreover, III/V semiconductors offer a wide range of opportunities to change the nanowire material composition, geometry and heterostructure design. This, in turn has a lot of implications, namely nanowires act as a test bed for detailed study of fundamental physics in low-dimensional systems as well as a perspective platform for numerous applications in nanoelectronics, optoelectronics, and spintronics 1-4 . The quantization in the potential landscape of a nanowire is ruled by both the Schroedinger and Poisson equations with appropriate boundary conditions at the surface. Thus, the state of a nanowire surface might strongly govern both charge carrier distribution and density within a nanowire. This apparently holds for InAs surface which is known for its high density of surface states in particular after exposure to air [5][6][7][8][9][10][11][12][13] . It is believed that due to the dominating donor-type surface states, supplying electrons to nanowire body, even intrinsic InAs nanowires have high n-type conductivity without additional doping [14][15][16][17][18][19][20][21][22][23][24] . In addition, low contact resistance of InAs nanowires 25 is another indication for the formation of an electron accumulation layer at the nanowire surface. It is natural to expect that the electron gas formed in InAs nanowires due to the surface states would possess different features depending on the surface states and the nanowire diameter 14,23,[26][27][28][29][30][31][32][33] . So far there exist several studies of electron and hole gas properties in core-shell nanowires, i.e. nano...

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Section: Theoretical Modelsupporting

confidence: 92%

“…In InAs nanowires with a wurtzite crystal structure the electron effective mass is larger, and the Fermi level pinning occurs at about 0.2 eV above the conduction band edge (ref. 41) opposite to 0.16 eV, as we considered. We do not expect any qualitative change of the results for the wurtzite-type InAs nanowires.…”

Section: Resultsmentioning

confidence: 99%

Features of electron gas in InAs nanowires imposed by interplay between nanowire geometry, doping and surface states

Degtyarev¹,

Khazanova²,

Demarina

2017

Sci Rep

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“…For both contact configurations, see legend, the conductance exhibits an overall increase at increasing V g with reproducible mesoscopic fluctuations. Sizable conductance G ∼ 2e 2 /h around V g = 0 is a consequence of the Fermi level pinning at the surface of InAs, which results in surface charge accumulation in our nominally undoped NWs 13,14 . Roughly linear V g dependence of G is consistent with previous measurements on these and other similar NWs 19 .…”

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confidence: 99%

Proximity effect and interface transparency in Al/InAs-nanowire/Al diffusive junctions

Bubis

Piatrusha

et al. 2017

Semicond. Sci. Technol.

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We investigate the proximity effect in InAs nanowire (NW) junctions with superconducting contacts made of Al. The carrier density in InAs is tuned by means of the back gate voltage Vg. At high positive Vg the devices feature transport signatures characteristic of diffusive junctions with highly transparent interfaces -sizable excess current, re-entrant resistance effect and proximity gap values (∆N ) close to the Al gap (∆0). At decreasing Vg, we observe a reduction of the proximity gap down to ∆N ≈ ∆0/2 at NW conductances ∼ 2e 2 /h, which is interpreted in terms of carrier density dependent reduction of the Al/InAs interface transparency. We demonstrate that the experimental behavior of ∆N is closely reproduced by a model with shallow potential barrier at the Al/InAs interface.A possibility to interface a superconductor (S) with a metallic (N) state of InAs-based mesoscopic semiconductors is known since at least two decades 1,2 . High critical and excess currents, sometimes comparable to a theoretical upper limit, are reliably observed in InAs nanowire (NW) Josephson junctions 3-5 . Observations of signatures of a Cooper pair splitting 6,7 further conform with high device quality. A recent revival of interest in proximity effect in S-NW devices emerged in the course of a search for Majorana zero-energy states 8 , with the research targeted at single conduction channel NWs 9-12 .Thanks to a well-known Fermi level pinning effect, which results in a charge accumulation at the surface of InAs 13,14 , the NWs grown from this material typically exhibit low contact resistance to normal metals. For the superconducting hybrid devices, however, even a weak interface reflectivity can sufficiently degrade the performance by suppressing the Andreev reflection in favor of the normal quasiparticle scattering 15,16 . Although the transparency of the S/NW interfaces can be controlled by various chemical treatments prior to the deposition of the superconductor 3-5,17 or, alternatively, via the in-situ MBE growth of the superconductor 18 , residual imperfections are still present 19,20 . One might expect that the underlying physics can be clarified by tracking the carrier density dependence of the proximity effect, since the effective interface transparency should critically depend on the shape of the potential barrier.In this work we study the evolution of the superconducting proximity effect in an InAs NW with evaporated Al contacts as a function of electron density in InAs, which is controlled by means of a global back gate. At high carrier densities, the transport data is compatible with highly transparent Al/InAs interfaces and the induced proximity gap (∆ N ) is close to the superconducting gap value in Al (∆ 0 ). The observed reduction of ∆ N by a factor of two at decreasing carrier density indicates gate-tunable interface transparency, which can be explained assuming a shallow potential barrier formed at the Al/InAs interface.We investigate unintentionally doped catalyst free InAs NWs grown by MBE on a Si(111) substrate. ...

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“…5. For bare InAs nanowires, it has been reported that the energy difference between near band-edge emission and surface-related emission is approximately ~ 35–45 meV [21]. However, for InGaAs nanowires, because the surface band bending is significantly reduced with increasing Ga composition, this energy difference would decrease simultaneously, and then electrons are less confined near the nanowire surface and holes are less localized at the nanowire center.…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, for nanowires of some narrow-gap materials (such as InAs, In−rich InGaAs), the high density of surface states can lead to a bend of the electronic band structure near the nanowire surface (surface Fermi level pinned effect). Such a non-flat band structure will further cause charge carrier redistribution, which can strongly hinder the performance of optical nanowire-based devices [21]. Therefore, eliminating these surface states is highly necessary.…”

Section: Introductionmentioning

confidence: 99%

Self-Seeded MOCVD Growth and Dramatically Enhanced Photoluminescence of InGaAs/InP Core–Shell Nanowires

Chen

Yang

et al. 2018

Nanoscale Res Lett

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We report on the growth and characterization of InGaAs/InP core–shell nanowires on Si–(111) substrates by metal-organic chemical vapor deposition (MOCVD). The strain at the core–shell interface induced by the large lattice mismatch between the InGaAs core and InP shell materials has strong influence on the growth behavior of the InP shell, leading to the asymmetric growth of InP shell around the InGaAs core and even to the bending of the nanowires. Transmission electron microscopy (TEM) measurements reveal that the InP shell is coherent with the InGaAs core without any misfit dislocations. Furthermore, photoluminescence (PL) measurements at 77 K show that the PL peak intensity from the InGaAs/InP core−shell nanowires displays a ∼ 100 times enhancement compared to the only InGaAs core sample without InP shell due to the passivation of surface states and effective carrier confinement resulting from InP shell layer. The results obtained here further our understanding of the growth behavior of strained core–shell heterostructure nanowires and may open new possibilities for applications in InGaAs/InP heterostructure nanowire-based optoelectronic devices on Si platform.

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Direct Measurements of Fermi Level Pinning at the Surface of Intrinsically n-Type InGaAs Nanowires

Cited by 66 publications

References 45 publications

Features of electron gas in InAs nanowires imposed by interplay between nanowire geometry, doping and surface states

Features of electron gas in InAs nanowires imposed by interplay between nanowire geometry, doping and surface states

Proximity effect and interface transparency in Al/InAs-nanowire/Al diffusive junctions

Self-Seeded MOCVD Growth and Dramatically Enhanced Photoluminescence of InGaAs/InP Core–Shell Nanowires

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