We report on the fabrication and electrical characterization of field-effect
devices based on wire-shaped InP crystals grown from Au catalyst particles by a
vapor-liquid-solid process. Our InP wires are n-type doped with diameters in
the 40-55 nm range and lengths of several microns. After being deposited on an
oxidized Si substrate, wires are contacted individually via e-beam fabricated
Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor
temperature dependence. The distance between the electrodes varies between 0.2
and 2 micron. The electron density in the wires is changed with a back gate.
Low-temperature transport measurements show Coulomb-blockade behavior with
single-electron charging energies of ~1 meV. We also demonstrate energy
quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure

Bakkers, E. P. A. M.

De Franceschi, S.

Feiner, L. F.

Gurevich, L.

Kouwenhoven, L. P.

van Dam, J. A.

English

arXiv

S. De Franceschi

J. A. van Dam

E. P. A. M. Bakkers

L. F. Feiner

L. Gurevich

L. P. Kouwenhoven

Crossref

Single-electron tunneling in InP nanowires

A study was performed on single-electron tunneling in InP nanowires. The contact resistances as low as ∼10 kω, with minor temperature dependence were obtained. The Coulomb-blockade behavior was shown with single-electron charging energies of ∼1 meV.</p

Van Dam, J. A.

Bakkers, E. P.A.M.

VBN (Videnbasen)  Aalborg Universitets forskningsportal

We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor–liquid–solid process. Our InP wires are n-type doped with diameters in the 40–55-nm range and lengths of several micrometers. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ? 10?k?, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 ?m. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ? 1?meV. We also demonstrate energy quantization resulting from the confinement in the wire.Kavli Institute of NanoscienceApplied Science

De Franceschi, S. (author)

Van Dam, J.A. (author)

Bakkers, E.P.A.M. (author)

Feiner, L.F. (author)

Gurevich, L. (author)

Kouwenhoven, P. (author)

TU Delft Repository

A study was performed on single-electron tunneling in InP nanowires. The contact resistances as low as ~10 k¿, with minor temperature dependence were obtained. The Coulomb-blockade behavior was shown with single-electron charging energies of ~1 meV

Franceschi, De, S.

Dam, Van, J.A.

Bakkers, E.P.A.M.

Feiner, L.F.

Kouwenhoven, L.P.

Pure OAI Repository

 Single-electron tunneling in InP nanowiresCitation for published version (APA):Franceschi, De, S., Dam, Van, J. A., Bakkers, E. P. A. M., Feiner, L. F., Gurevich, L., & Kouwenhoven, L. P.(2003). Single-electron tunneling in InP nanowires. Applied Physics Letters, 83(2), 344-346.https://doi.org/10.1063/1.1590426DOI:10.1063/1.1590426Document status and date:Published: 01/01/2003Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 05. Oct. 2023APPLIED PHYSICS LETTERS VOLUME 83, NUMBER 2 14 JULY 2003DownSingle-electron tunneling in InP nanowiresS. De Franceschia) and J. A. van DamDepartment of NanoScience and ERATO Mesoscopic Correlation Project, Delft University of Technology,PO Box 5046, 2600 GA Delft, The NetherlandsE. P. A. M. Bakkers and L. F. FeinerPhilips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The NetherlandsL. Gurevich and L. P. KouwenhovenDepartment of NanoScience and ERATO Mesoscopic Correlation Project, Delft University of Technology,PO Box 5046, 2600 GA Delft, The Netherlands~Received 30 January 2003; accepted 7 May 2003!We report on the fabrication and electrical characterization of field-effect devices based onwire-shaped InP crystals grown from Au catalyst particles by a vapor–liquid–solid process. Our InPwires aren-type doped with diameters in the 40–55-nm range and lengths of several micrometers.After being deposited on an oxidized Si substrate, wires are contacted individually via e-beamfabricated Ti/Al electrodes. We obtain contact resistances as low as;10 kV, with minortemperature dependence. The distance between the electrodes varies between 0.2 and 2mm. Theelectron density in the wires is changed with a back gate. Low-temperature transport measurementsshow Coulomb-blockade behavior with single-electron charging energies of;1 meV. We alsodemonstrate energy quantization resulting from the confinement in the wire. ©2003 AmericanInstitute of Physics.@DOI: 10.1063/1.1590426#ngoserdeateatisseeeoructnx-eirroWnorL/hedP.aating.inos-e isofpat-ndi-dtedreere-eal-c-m-AChemically synthesized semiconductor nanowires~ornanowhiskers! are attracting increasing interest as buildiblocks for a bottom-up approach to the fabrication of nancale devices and sensors. A key property of these matsystems is the unique versatility in terms of geometricalmensions and composition. Nanowires have already bgrown from several semiconductor materials~group-IVelements,1,2 III-V, 3–6 and II-VI compounds7!, includingstructures with variable doping and composition, suchn-type/p-type InP,8 InAs/InP,5 GaAs/GaP,8 and Si/SiGe.2 Thegrowth technique is based on the vapor–liquid–solid~VLS!process9 occurring at metallic catalysts, such as nanomesized Au particles. The nanowire diameter is set by the clyst dimension, typically 10–100 nm. The nanowire lengthproportional to the growth time and can exceed hundredmicrometers. The semiconductor is provided either by malorganic vapor-phase sources,3,5 or by laser ablation.10Many room-temperature applications have already bshown, such as single-nanowire field-effect transist~FETs!,4 diodes,8 and logic gates11 combining bothn-typeand p-type nanowires. Very recently, nanowire heterostrtures have been operated as resonant tunneling diodes aK.12 Yet, the low-temperature properties of nanowires atheir potential for quantum devices are still widely uneplored.In this letter, we describe the realization of FET devicfrom individual n-type InP nanowires. We discuss thetransport properties down to 0.35 K, where single-electtunneling and quantum effects can play a dominant role.also provide details on the fabrication of the electrical cotacts to the nanowires, a crucial aspect of the present wOur InP nanowires are grown via the laser-assisted Va!Electronic mail: silvano@qt.tn.tudelft.nl3440003-6951/2003/83(2)/344/3/$20.00loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licens-iali-ensr-a-oft-ns-4.2dsne-k.Smethod. A pulsed laser~193-nm ArF laser, 10 Hz, 100 mJpulse! is used to ablate from a pressed InP powder enricwith 1 mol % of Se, which acts as a donor impurity in InNanowires grow from Au seeds formed after annealing2-Å-equivalent Au film deposited on a Si substrate withsuperficial native oxide. During growth time (;30 min) thesubstrate temperature is kept at 475 °C. The resulnanowires are 5–10mm long with a diameter of 40–55 nmImmediately after growth, the nanowires are dispersedchlorobenzene. A few droplets of this dispersion are depited on ap1 Si substrate with a 250-nm-thick SiO2 over-layer. To favor the adhesion of the nanowires, the surfacfunctionalized with a self-assembled monolayer3-aminopropyltriethoxysilane~APTES!.13 Optical imaging isused to locate the nanowires with respect to a referencetern of predefined Pt markers. The nanowires are then ividually contacted with a pair of metal electrodes~sourceand drain leads! defined by electron-beam lithography~seeupper inset to Fig. 1!. The distanceL between the source andrain electrodes is varied between 0.2 and 2mm.The contact electrodes consist of thermally evaporaTi~100 nm!/Al ~20 nm!. Before metal deposition, samples atreated with BHF for 20 s in order to etch the oxide layaround the nanowires.14 As-deposited contacts show high rsistance, typically in excess of 10 GV. The contact resistancimproves drastically after forming-gas rapid thermal anneing at 475 °C for 60 s~for a discussion of the interface reation between Ti and InP we refer to Ref. 15!.We have characterized over ten devices at different teperaturesT. At room temperature,I –V characteristics arelinear ~see dashed lines in Fig. 1!, with resistancesR as lowas 30 kV. Despite sample-to-sample fluctuations,R appearsto increase withL, as shown in the lower inset to Fig. 1.linear fit yieldsR540 kV145 kV/mm3L, where the con-© 2003 American Institute of Physicse or copyright; see http://apl.aip.org/about/rights_and_permissionsustaaAseraboccvethaknitetes-rdtoveryll-f-gc--tates:dee-, asr astemssesnceomrotuTentn ac.345Appl. Phys. Lett., Vol. 83, No. 2, 14 July 2003 De Franceschi et al.Downstant term and the slope coefficient can be taken as roestimates of the total contact resistance and the wire resiity, respectively.Below a few Kelvin, theI –V characteristics developnonlinearity around zero bias. This behavior, common tomeasured devices, is shown in Fig. 1 for device(L50.20mm), and B (L51.95mm), respectively theshortest and longest devices measured. The zero-biaspression of the conductance has a pronounced dependon the voltageVg applied to thep1 Si substrate. This is acharacteristic fingerprint of Coulomb-blockaded transpowhich becomes dominant at low temperatures. In fact,electronic island, formed inside the nanowire segmenttween source and drain electrodes, leads to Coulomb blade of transport whenkBT,e2/C, whereC is the total ca-pacitance of the island.16 At source–drain voltages,Vsd,larger thane/C, the slope of the low-T trace is close to thecorresponding room-T value, indicating littleT-dependenceof the contact resistance.Figure 2~a! shows conductanceG versusVg for device C(L50.65mm) and D (L51.6 mm, inset!. Both traces ex-hibit sharp peaks corresponding to Coulomb-blockade oslations. This clearly demonstrates that we have achiesingle-electron control over the electronic charge andtransport properties of the nanowire. The Coulomb pehave irregularly distributed sizes, and theirVg-spacing variesconsiderably, suggesting the formation of more than oelectronic island along the nanowire. This interpretationsupported by the measurement shown in Fig. 2~b! where thedifferential conductancedI/dVsd of device C is plotted ongray scale as a function of (Vg , Vsd). In this plot, Coulombblockade takes place within dark regions with the characistic diamond shape. In some cases, such as forVg between240 and290 mV, Coulomb diamonds are clearly separafrom each other and have all their edges fully defined. Thicharacteristic of Coulomb-blockaded transport throughsingle electronic island. In otherVg-regions, however, diamonds overlap with each other, as we would expect foFIG. 1. I –V characteristics at room temperature~dashed lines! and 0.35 K~solid lines!, for devices A and B. Upper inset: scanning-electron micgraph of device B. Lower inset: length dependence of the room-temperasource–drain resistance. Each solid circle refers to a different device.dashed line is a linear fit.loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licensghiv-llup-ncet,ne-k-il-desesr-disaananowire containing more than one~most likely two! islandsin series. TheVg-dependent alternation of single- andouble-island regimes, shown in Fig. 2~b!, is representativeof the general behavior in our devices. We would likestress that such charge reconfigurations are found to bestable and reproducible.Each Coulomb diamond is associated with a wedefined numberN of confined electrons. From the halheight ~along Vsd) of the diamonds we estimate a charginenergy e2/C;1 meV. The Vg-width of the diamonds isaround 10–20 mV, from which we deduceCg /C'1/7,whereCg is the capacitance to the back gate.17 This impliesthatN decreases by;100 when moving from right to left inFig. 2~a!. Based on separate studies,18 we believe this is stillonly a small fraction of the total amount of conduction eletrons in the nanowire.We now focus on a smallVg-range where device C exhibits single-island behavior. Figure 3 shows severaldI/dVsdvs Vg traces taken at different values ofVsd between 0 and20.6 mV. The lowest trace (Vsd50) shows two Coulombpeaks denoting transitions between successive charge say fromN21 to N ~left peak!, and fromN to N11 ~rightpeak!. At finite bias, each peak indI/dVsd splits proportion-ally to Vsd, as expected from ordinary Coulomb-blockatheory. The left-moving~right-moving! split-peak corre-sponds to the onset of tunneling from~to! the source~drain!lead. Interestingly, at largerVsd, extra resonances appear btween the split-peaks. IncreasingVsd, the Vg-positions ofsuch resonances evolve parallel to one of the split-peaksemphasized by dashed lines. We recognize this behaviocharacteristic of transport through a quantum-dot syswith a discrete energy spectrum.19 The two extra resonancecan be readily explained as the result of tunneling procesinvolving excited states of the quantum dot. The resonaon the right side of Fig. 3 denotes the onset of tunneling fr-reheFIG. 2. ~a! ConductanceG versus back-gate voltageVg measured at 0.35 Kwith a dc biasVsd520 mV. The two traces refer to devices C and D~inset!.~b! Gray-scale plot of differential conductancedI/dVsd versus (Vg , Vsd).dI/dVsd increases when going from dark to light gray. The measuremrefers to device C, and was taken at 0.35 K with a lock-in technique at abias excitation of 20mV. Inset: scanning electron micrograph of device Ce or copyright; see http://apl.aip.org/about/rights_and_permissionstoichssrgthena-theuihe-de-cialAidci-tion.H.hys.er,r,R.J.ys., re-ireppl.omtonts,con-. J..esimet346 Appl. Phys. Lett., Vol. 83, No. 2, 14 July 2003 De Franceschi et al.Downthe source lead to the first excited state withN11 electrons~see top-right inset!. The one on the left can be ascribedthe tunneling of an electron from the dot to the drain, whleaves the dot in an excited state withN21 electrons~seetop-left inset!. The bias voltage for which the resonance asociated to anN-electron excited-state begins to emerge idirect measurement of the corresponding excitation eneDE(N). We find DE(N21)'0.36 MeV and DE(N11)'0.30 meV.Another sign of energy quantization is based onT-dependence of the conductance peaks atVsd50. As ex-pected for single-electron tunneling in quantum dots, lowing T gives an increased peak height as a result of resotunneling.16 This is, in fact, observed in the low-T limit ~datanot shown!. The full width at half-maximum increases linearly with T, but with two different slopes, associated withe quantum (kBT,DE) and the classical (kBT.DE)regime.20 In our case, the transition between the two regimoccurs at about 1.2 K@see Fig. 3~b!# corresponding toDE;0.1 meV, in agreement with the previous findings. Oobservation of a discrete energy spectrum represents anFIG. 3. dI/dVsd vs Vg , for different dc values ofVsd, from 0 ~lower trace!to 20.6 mV ~upper trace! in steps of20.02 mV. Dashed lines indicate thevolution of the peaks associated with tunneling via excited states. Aplified picture of the corresponding processes is given in the top insBottom inset: full width at half-maximumw vs temperatureT for the leftCoulomb peak atVsd50. The solid~dashed! line is the theoretical predic-tion, w5(C/eCg)33.52kBT @w5(C/eCg)34.35kBT#, for the quantum~classical! regime ~see Ref. 20!. We usedC/Cg57.35, obtained from theVsd-dependence of theVg-splitting.loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licens-ay,er-ntsrm-portant premise for a deeper investigation of quantum pnomena and the development of controllable quantumvices based on semiconductor nanowires.The authors thank T. Nolst Trenite´ and S. Tarucha forhelp and discussions. The authors acknowledge finansupport from the Specially Promoted Research, Grant-in-for Scientific Research, from the Ministry of Education, Sence and Culture in Japan, and from the Dutch Organizafor Fundamental Research on Matter~FOM!.1Y. Cui and C. M. Lieber, Science291, 851 ~2001!.2Y. Wu, R. Fan, and P. Yang, Nano Lett.2, 83 ~2002!.3K. Hiruma, M. Yazawa, T. Katsuyama, K. Ogawa, K. Haraguchi, MKoguchi, and H. Kakibayashi, J. Appl. Phys.77, 447 ~1995!.4X. Duan, Y. Huang, Y. Cui, J. Wang, and C. M. Lieber, Nature~London!409, 66 ~2001!.5M. T. Björk, B. J. Ohlsson, T. Sass, A. I. Persson, C. Thelander, M.Magnusson, K. Deppert, L. R. Wallenberg, and L. Samuelson, Appl. PLett. 80, 1058~2002!.6Y. Huang, X. Duan, Y. Cui, and C. M. Lieber, Nano Lett.2, 101 ~2002!.7R. Solanki, J. Huo, J. L. Freeouf, and B. Miner, Appl. Phys. Lett.81, 3864~2002!.8M. S. Gudiksen, L. J. Lauhon, J. Wang, D. C. Smith, and C. M. LiebNature~London! 415, 617 ~2002!.9R. S. Wagner and W. C. Ellis, Appl. Phys. Lett.4, 89 ~1964!.10A. M. Morales and C. M. Lieber, Science279, 208 ~1998!.11Y. Huang, X. Duan, Y. Cui, L. J. Lauhon, K.-H. Kim, and C. M. LiebeScience294, 1313~2001!.12M. T. Björk, B. J. Ohlsson, C. Thelander, A. I. Persson, K. Deppert, L.Wallenberg, and L. Samuelson, Appl. Phys. Lett.81, 4458~2002!.13J. Liu, M. J. Casavant, M. Cox, D. A. Walters, P. Boul, W. Lu, A.Rimberg, K. A. Smith, D. T. Colbert, and R. E. Smalley, Chem. PhLipids 303, 125 ~1999!.14High-resolution images, obtained by transmission-electron microscopyvealed an oxide thickness up to 10 nm, with considerable wire-to-wvariations.15M. B. Takeyama, A. Noya, T. Hashizume, and H. Hasegawa, Jpn. J. APhys.38, 1115~1999!.16Single Charge Tunneling, edited by H. Grabert and M. H. Devoret~Ple-num, New York, 1992!.17From a simplified model we estimateCg'@2pee0 /ln(2d/R)#3L0, whereL0 is the length of a cylindrical electronic island,e54 ~relative dielectricconstant for SiO2), R520 nm~island radius!, d5250 nm~distance to theback gate!. Then, U5e2/C51 meV andCg /C51/7 yield L0'0.3 mm&L.18We studied the pinch-off characteristic of similar devices, fabricated frthe same batch of nanowires. Using a simple electrostatics model~se ,e.g., Ref. 6!, we estimated a linear density of;104 electrons/mm. Ne-glecting surface-induced depletion, this corresponds;1019 electrons/cm3. Secondary-ion mass-spectroscopy measuremeperformed on a massive amount of nanowires grown under the sameditions, gave a Se content of 1019– 1020 atoms/cm3.19A. T. Johnson, L. P. Kouwenhoven, W. de Jong, N. C. van der Vaart, CP. M. Harmans, and C. T. Foxon, Phys. Rev. Lett.69, 1592~1992!.20E. B. Foxman, U. Meirav, P. L. McEuen, M. A. Kastner, O. Klein, P. ABelk, D. M. Abusch, and S. J. Wind, Phys. Rev. B50, 14193~1994!.-s.e or copyright; see http://apl.aip.org/about/rights_and_permissions

Franceschi, S  De

Dam, JA  Van

Bakkers, EPAM Erik

Feiner, LF

Gurevich, L

Kouwenhoven, Leo P

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 Single-electron tunneling in InP nanowiresCitation for published version (APA):Franceschi, De, S., Dam, Van, J. A., Bakkers, E. P. A. M., Feiner, L. F., Gurevich, L., & Kouwenhoven, L. P.(2003). Single-electron tunneling in InP nanowires. Applied Physics Letters, 83(2), 344-346.https://doi.org/10.1063/1.1590426DOI:10.1063/1.1590426Document status and date:Published: 01/01/2003Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 04. Oct. 2023APPLIED PHYSICS LETTERS VOLUME 83, NUMBER 2 14 JULY 2003DownSingle-electron tunneling in InP nanowiresS. De Franceschia) and J. A. van DamDepartment of NanoScience and ERATO Mesoscopic Correlation Project, Delft University of Technology,PO Box 5046, 2600 GA Delft, The NetherlandsE. P. A. M. Bakkers and L. F. FeinerPhilips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The NetherlandsL. Gurevich and L. P. KouwenhovenDepartment of NanoScience and ERATO Mesoscopic Correlation Project, Delft University of Technology,PO Box 5046, 2600 GA Delft, The Netherlands~Received 30 January 2003; accepted 7 May 2003!We report on the fabrication and electrical characterization of field-effect devices based onwire-shaped InP crystals grown from Au catalyst particles by a vapor–liquid–solid process. Our InPwires aren-type doped with diameters in the 40–55-nm range and lengths of several micrometers.After being deposited on an oxidized Si substrate, wires are contacted individually via e-beamfabricated Ti/Al electrodes. We obtain contact resistances as low as;10 kV, with minortemperature dependence. The distance between the electrodes varies between 0.2 and 2mm. Theelectron density in the wires is changed with a back gate. Low-temperature transport measurementsshow Coulomb-blockade behavior with single-electron charging energies of;1 meV. We alsodemonstrate energy quantization resulting from the confinement in the wire. ©2003 AmericanInstitute of Physics.@DOI: 10.1063/1.1590426#ngoserdeateatisseeeoructnx-eirroWnorL/hedP.aating.inos-e isofpat-ndi-dtedreere-eal-c-m-AChemically synthesized semiconductor nanowires~ornanowhiskers! are attracting increasing interest as buildiblocks for a bottom-up approach to the fabrication of nancale devices and sensors. A key property of these matsystems is the unique versatility in terms of geometricalmensions and composition. Nanowires have already bgrown from several semiconductor materials~group-IVelements,1,2 III-V, 3–6 and II-VI compounds7!, includingstructures with variable doping and composition, suchn-type/p-type InP,8 InAs/InP,5 GaAs/GaP,8 and Si/SiGe.2 Thegrowth technique is based on the vapor–liquid–solid~VLS!process9 occurring at metallic catalysts, such as nanomesized Au particles. The nanowire diameter is set by the clyst dimension, typically 10–100 nm. The nanowire lengthproportional to the growth time and can exceed hundredmicrometers. The semiconductor is provided either by malorganic vapor-phase sources,3,5 or by laser ablation.10Many room-temperature applications have already bshown, such as single-nanowire field-effect transist~FETs!,4 diodes,8 and logic gates11 combining bothn-typeand p-type nanowires. Very recently, nanowire heterostrtures have been operated as resonant tunneling diodes aK.12 Yet, the low-temperature properties of nanowires atheir potential for quantum devices are still widely uneplored.In this letter, we describe the realization of FET devicfrom individual n-type InP nanowires. We discuss thetransport properties down to 0.35 K, where single-electtunneling and quantum effects can play a dominant role.also provide details on the fabrication of the electrical cotacts to the nanowires, a crucial aspect of the present wOur InP nanowires are grown via the laser-assisted Va!Electronic mail: silvano@qt.tn.tudelft.nl3440003-6951/2003/83(2)/344/3/$20.00loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licens-iali-ensr-a-oft-ns-4.2dsne-k.Smethod. A pulsed laser~193-nm ArF laser, 10 Hz, 100 mJpulse! is used to ablate from a pressed InP powder enricwith 1 mol % of Se, which acts as a donor impurity in InNanowires grow from Au seeds formed after annealing2-Å-equivalent Au film deposited on a Si substrate withsuperficial native oxide. During growth time (;30 min) thesubstrate temperature is kept at 475 °C. The resulnanowires are 5–10mm long with a diameter of 40–55 nmImmediately after growth, the nanowires are dispersedchlorobenzene. A few droplets of this dispersion are depited on ap1 Si substrate with a 250-nm-thick SiO2 over-layer. To favor the adhesion of the nanowires, the surfacfunctionalized with a self-assembled monolayer3-aminopropyltriethoxysilane~APTES!.13 Optical imaging isused to locate the nanowires with respect to a referencetern of predefined Pt markers. The nanowires are then ividually contacted with a pair of metal electrodes~sourceand drain leads! defined by electron-beam lithography~seeupper inset to Fig. 1!. The distanceL between the source andrain electrodes is varied between 0.2 and 2mm.The contact electrodes consist of thermally evaporaTi~100 nm!/Al ~20 nm!. Before metal deposition, samples atreated with BHF for 20 s in order to etch the oxide layaround the nanowires.14 As-deposited contacts show high rsistance, typically in excess of 10 GV. The contact resistancimproves drastically after forming-gas rapid thermal anneing at 475 °C for 60 s~for a discussion of the interface reation between Ti and InP we refer to Ref. 15!.We have characterized over ten devices at different teperaturesT. At room temperature,I –V characteristics arelinear ~see dashed lines in Fig. 1!, with resistancesR as lowas 30 kV. Despite sample-to-sample fluctuations,R appearsto increase withL, as shown in the lower inset to Fig. 1.linear fit yieldsR540 kV145 kV/mm3L, where the con-© 2003 American Institute of Physicse or copyright; see http://apl.aip.org/about/rights_and_permissionsustaaAseraboccvethaknitetes-rdtoveryll-f-gc--tates:dee-, asr astemssesnceomrotuTentn ac.345Appl. Phys. Lett., Vol. 83, No. 2, 14 July 2003 De Franceschi et al.Downstant term and the slope coefficient can be taken as roestimates of the total contact resistance and the wire resiity, respectively.Below a few Kelvin, theI –V characteristics developnonlinearity around zero bias. This behavior, common tomeasured devices, is shown in Fig. 1 for device(L50.20mm), and B (L51.95mm), respectively theshortest and longest devices measured. The zero-biaspression of the conductance has a pronounced dependon the voltageVg applied to thep1 Si substrate. This is acharacteristic fingerprint of Coulomb-blockaded transpowhich becomes dominant at low temperatures. In fact,electronic island, formed inside the nanowire segmenttween source and drain electrodes, leads to Coulomb blade of transport whenkBT,e2/C, whereC is the total ca-pacitance of the island.16 At source–drain voltages,Vsd,larger thane/C, the slope of the low-T trace is close to thecorresponding room-T value, indicating littleT-dependenceof the contact resistance.Figure 2~a! shows conductanceG versusVg for device C(L50.65mm) and D (L51.6 mm, inset!. Both traces ex-hibit sharp peaks corresponding to Coulomb-blockade oslations. This clearly demonstrates that we have achiesingle-electron control over the electronic charge andtransport properties of the nanowire. The Coulomb pehave irregularly distributed sizes, and theirVg-spacing variesconsiderably, suggesting the formation of more than oelectronic island along the nanowire. This interpretationsupported by the measurement shown in Fig. 2~b! where thedifferential conductancedI/dVsd of device C is plotted ongray scale as a function of (Vg , Vsd). In this plot, Coulombblockade takes place within dark regions with the characistic diamond shape. In some cases, such as forVg between240 and290 mV, Coulomb diamonds are clearly separafrom each other and have all their edges fully defined. Thicharacteristic of Coulomb-blockaded transport throughsingle electronic island. In otherVg-regions, however, diamonds overlap with each other, as we would expect foFIG. 1. I –V characteristics at room temperature~dashed lines! and 0.35 K~solid lines!, for devices A and B. Upper inset: scanning-electron micgraph of device B. Lower inset: length dependence of the room-temperasource–drain resistance. Each solid circle refers to a different device.dashed line is a linear fit.loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licensghiv-llup-ncet,ne-k-il-desesr-disaananowire containing more than one~most likely two! islandsin series. TheVg-dependent alternation of single- andouble-island regimes, shown in Fig. 2~b!, is representativeof the general behavior in our devices. We would likestress that such charge reconfigurations are found to bestable and reproducible.Each Coulomb diamond is associated with a wedefined numberN of confined electrons. From the halheight ~along Vsd) of the diamonds we estimate a charginenergy e2/C;1 meV. The Vg-width of the diamonds isaround 10–20 mV, from which we deduceCg /C'1/7,whereCg is the capacitance to the back gate.17 This impliesthatN decreases by;100 when moving from right to left inFig. 2~a!. Based on separate studies,18 we believe this is stillonly a small fraction of the total amount of conduction eletrons in the nanowire.We now focus on a smallVg-range where device C exhibits single-island behavior. Figure 3 shows severaldI/dVsdvs Vg traces taken at different values ofVsd between 0 and20.6 mV. The lowest trace (Vsd50) shows two Coulombpeaks denoting transitions between successive charge say fromN21 to N ~left peak!, and fromN to N11 ~rightpeak!. At finite bias, each peak indI/dVsd splits proportion-ally to Vsd, as expected from ordinary Coulomb-blockatheory. The left-moving~right-moving! split-peak corre-sponds to the onset of tunneling from~to! the source~drain!lead. Interestingly, at largerVsd, extra resonances appear btween the split-peaks. IncreasingVsd, the Vg-positions ofsuch resonances evolve parallel to one of the split-peaksemphasized by dashed lines. We recognize this behaviocharacteristic of transport through a quantum-dot syswith a discrete energy spectrum.19 The two extra resonancecan be readily explained as the result of tunneling procesinvolving excited states of the quantum dot. The resonaon the right side of Fig. 3 denotes the onset of tunneling fr-reheFIG. 2. ~a! ConductanceG versus back-gate voltageVg measured at 0.35 Kwith a dc biasVsd520 mV. The two traces refer to devices C and D~inset!.~b! Gray-scale plot of differential conductancedI/dVsd versus (Vg , Vsd).dI/dVsd increases when going from dark to light gray. The measuremrefers to device C, and was taken at 0.35 K with a lock-in technique at abias excitation of 20mV. Inset: scanning electron micrograph of device Ce or copyright; see http://apl.aip.org/about/rights_and_permissionstoichssrgthena-theuihe-de-cialAidci-tion.H.hys.er,r,R.J.ys., re-ireppl.omtonts,con-. J..esimet346 Appl. Phys. Lett., Vol. 83, No. 2, 14 July 2003 De Franceschi et al.Downthe source lead to the first excited state withN11 electrons~see top-right inset!. The one on the left can be ascribedthe tunneling of an electron from the dot to the drain, whleaves the dot in an excited state withN21 electrons~seetop-left inset!. The bias voltage for which the resonance asociated to anN-electron excited-state begins to emerge idirect measurement of the corresponding excitation eneDE(N). We find DE(N21)'0.36 MeV and DE(N11)'0.30 meV.Another sign of energy quantization is based onT-dependence of the conductance peaks atVsd50. As ex-pected for single-electron tunneling in quantum dots, lowing T gives an increased peak height as a result of resotunneling.16 This is, in fact, observed in the low-T limit ~datanot shown!. The full width at half-maximum increases linearly with T, but with two different slopes, associated withe quantum (kBT,DE) and the classical (kBT.DE)regime.20 In our case, the transition between the two regimoccurs at about 1.2 K@see Fig. 3~b!# corresponding toDE;0.1 meV, in agreement with the previous findings. Oobservation of a discrete energy spectrum represents anFIG. 3. dI/dVsd vs Vg , for different dc values ofVsd, from 0 ~lower trace!to 20.6 mV ~upper trace! in steps of20.02 mV. Dashed lines indicate thevolution of the peaks associated with tunneling via excited states. Aplified picture of the corresponding processes is given in the top insBottom inset: full width at half-maximumw vs temperatureT for the leftCoulomb peak atVsd50. The solid~dashed! line is the theoretical predic-tion, w5(C/eCg)33.52kBT @w5(C/eCg)34.35kBT#, for the quantum~classical! regime ~see Ref. 20!. We usedC/Cg57.35, obtained from theVsd-dependence of theVg-splitting.loaded 12 Aug 2010 to 131.155.151.8. Redistribution subject to AIP licens-ay,er-ntsrm-portant premise for a deeper investigation of quantum pnomena and the development of controllable quantumvices based on semiconductor nanowires.The authors thank T. Nolst Trenite´ and S. Tarucha forhelp and discussions. The authors acknowledge finansupport from the Specially Promoted Research, Grant-in-for Scientific Research, from the Ministry of Education, Sence and Culture in Japan, and from the Dutch Organizafor Fundamental Research on Matter~FOM!.1Y. Cui and C. M. Lieber, Science291, 851 ~2001!.2Y. Wu, R. Fan, and P. Yang, Nano Lett.2, 83 ~2002!.3K. Hiruma, M. Yazawa, T. Katsuyama, K. Ogawa, K. Haraguchi, MKoguchi, and H. Kakibayashi, J. Appl. Phys.77, 447 ~1995!.4X. Duan, Y. Huang, Y. Cui, J. Wang, and C. M. Lieber, Nature~London!409, 66 ~2001!.5M. T. Björk, B. J. Ohlsson, T. Sass, A. I. Persson, C. Thelander, M.Magnusson, K. Deppert, L. R. Wallenberg, and L. Samuelson, Appl. PLett. 80, 1058~2002!.6Y. Huang, X. Duan, Y. Cui, and C. M. Lieber, Nano Lett.2, 101 ~2002!.7R. Solanki, J. Huo, J. L. Freeouf, and B. Miner, Appl. Phys. Lett.81, 3864~2002!.8M. S. Gudiksen, L. J. Lauhon, J. Wang, D. C. Smith, and C. M. LiebNature~London! 415, 617 ~2002!.9R. S. Wagner and W. C. Ellis, Appl. Phys. Lett.4, 89 ~1964!.10A. M. Morales and C. M. Lieber, Science279, 208 ~1998!.11Y. Huang, X. Duan, Y. Cui, L. J. Lauhon, K.-H. Kim, and C. M. LiebeScience294, 1313~2001!.12M. T. Björk, B. J. Ohlsson, C. Thelander, A. I. Persson, K. Deppert, L.Wallenberg, and L. Samuelson, Appl. Phys. Lett.81, 4458~2002!.13J. Liu, M. J. Casavant, M. Cox, D. A. Walters, P. Boul, W. Lu, A.Rimberg, K. A. Smith, D. T. Colbert, and R. E. Smalley, Chem. PhLipids 303, 125 ~1999!.14High-resolution images, obtained by transmission-electron microscopyvealed an oxide thickness up to 10 nm, with considerable wire-to-wvariations.15M. B. Takeyama, A. Noya, T. Hashizume, and H. Hasegawa, Jpn. J. APhys.38, 1115~1999!.16Single Charge Tunneling, edited by H. Grabert and M. H. Devoret~Ple-num, New York, 1992!.17From a simplified model we estimateCg'@2pee0 /ln(2d/R)#3L0, whereL0 is the length of a cylindrical electronic island,e54 ~relative dielectricconstant for SiO2), R520 nm~island radius!, d5250 nm~distance to theback gate!. Then, U5e2/C51 meV andCg /C51/7 yield L0'0.3 mm&L.18We studied the pinch-off characteristic of similar devices, fabricated frthe same batch of nanowires. Using a simple electrostatics model~se ,e.g., Ref. 6!, we estimated a linear density of;104 electrons/mm. Ne-glecting surface-induced depletion, this corresponds;1019 electrons/cm3. Secondary-ion mass-spectroscopy measuremeperformed on a massive amount of nanowires grown under the sameditions, gave a Se content of 1019– 1020 atoms/cm3.19A. T. Johnson, L. P. Kouwenhoven, W. de Jong, N. C. van der Vaart, CP. M. Harmans, and C. T. Foxon, Phys. Rev. Lett.69, 1592~1992!.20E. B. Foxman, U. Meirav, P. L. McEuen, M. A. Kastner, O. Klein, P. ABelk, D. M. Abusch, and S. J. Wind, Phys. Rev. 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We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor–liquid–solid process. Our InP wires are n-type doped with diameters in the 40–55-nm range and lengths of several micrometers. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ? 10?k?, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 ?m. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ? 1?meV. We also demonstrate energy quantization resulting from the confinement in the wire

Van Dam, J.A.

Kouwenhoven, P.

Single-electron tunneling in InP nanowires

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