The catalyst-free metal organic vapor phase epitaxialgrowth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowiregrowth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InPnanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.Peer reviewe

Hakkarainen, T.

Jiang, H.

Kauppinen, Esko I.

Lipsanen, Harri

Mattila, M.

Aaltodoc Publication Archive

This is an electronic reprint of the original article.This reprint may differ from the original in pagination and typographic detail.Author(s): Mattila, M. & Hakkarainen, T. & Lipsanen, Harri & Jiang, H. &Kauppinen, E. I.Title: Catalyst-free growth of In(As)P nanowires on siliconYear: 2006Version: Final published versionPlease cite the original version:Mattila, M. & Hakkarainen, T. & Lipsanen, Harri & Jiang, H. & Kauppinen, E. I. 2006.Catalyst-free growth of In(As)P nanowires on silicon. Applied Physics Letters. Volume89, Issue 6. P. 063119/1-3. ISSN 0003-6951 (printed). DOI: 10.1063/1.2336599.Rights: © 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other userequires prior permission of the author and the American Institute of Physics.http://scitation.aip.org/content/aip/journal/japAll material supplied via Aaltodoc is protected by copyright and other intellectual property rights, andduplication or sale of all or part of any of the repository collections is not permitted, except that material maybe duplicated by you for your research use or educational purposes in electronic or print form. You mustobtain permission for any other use. Electronic or print copies may not be offered, whether for sale orotherwise to anyone who is not an authorised user.Powered by TCPDF (www.tcpdf.org)Catalyst-free growth of In(As)P nanowires on siliconM. Mattila, T. Hakkarainen, H. Lipsanen, H. Jiang, and E. I. Kauppinen  Citation: Applied Physics Letters 89, 063119 (2006); doi: 10.1063/1.2336599 View online: http://dx.doi.org/10.1063/1.2336599 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/89/6?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Selective-area vapor-liquid-solid growth of tunable InAsP quantum dots in nanowires Appl. Phys. Lett. 98, 251101 (2011); 10.1063/1.3600777  Enhanced Sb incorporation in InAsSb nanowires grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 98, 113104 (2011); 10.1063/1.3566980  The influence of the droplet composition on the vapor-liquid-solid growth of InAs nanowires on GaAs ( 1 ¯ 1 ¯ 1 ¯) B by metal-organic vapor phase epitaxy J. Appl. Phys. 104, 114315 (2008); 10.1063/1.3033556  Metal free growth and characterization of InAs1−xPx nanowires AIP Conf. Proc. 893, 97 (2007); 10.1063/1.2729788  Enhanced luminescence from catalyst-free grown InP nanowires Appl. Phys. Lett. 90, 033101 (2007); 10.1063/1.2431711    This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:130.233.216.27 On: Mon, 04 May 2015 10:02:31Catalyst-free growth of In„As…P nanowires on siliconM. Mattila,a T. Hakkarainen, and H. LipsanenOptoelectronics Laboratory, Micronova, Helsinki University of Technology, P.O. Box 3500,FIN-02015 TKK, FinlandH. Jiang and E. I. KauppinenbVTT Technical Research Center of Finland, P.O. Box 1000, FIN-02044 VTT, FinlandReceived 30 May 2006; accepted 26 June 2006; published online 10 August 2006The catalyst-free metal organic vapor phase epitaxial growth of InAsP nanowires on siliconsubstrates is investigated using in situ deposited In droplets as seeds for nanowire growth. The thinsubstrate native oxide is found to play a crucial role in the nanowire formation. The structure of thenanowires is characterized by photoluminescence and electron microscopy measurements. Thecrystal structure of the InP nanowires is wurtzite with its c axis perpendicular to the nanowire axis.Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescencespectrum exhibiting peak at the InAsP and InP band gap energies. © 2006 American Institute ofPhysics. DOI: 10.1063/1.2336599The fabrication of one-dimensional nanostructures, ornanowires, has been under intense investigation due to theirlucrative device applications.1 One way of fabricating nano-wires is by the vapor-liquid-solid VLS method2 using metalorganic vapor phase epitaxy MOVPE.3 Typically, the fab-rication of III-V semiconductor nanowires by the VLSmethod has required the deposition of metal catalysts on thesubstrate either by evaporation, or from colloidal solutions oraerosols before actual growth. Very recently, Novotny andYu4 demonstrated the catalyst-free growth of InP nanowireson InP111 substrates by changing the substrate surface re-construction by annealing to support vertical nanowiregrowth at low temperatures. This catalyst-free method offersa possibility for totally self-assembled one-dimensionalnanostructure fabrication without any preprocessing.In this letter we have investigated the catalyst-free orself-catalyzed growth of InAsP nanowires on Si111 sub-strates using in situ deposited In metal droplets as seeds fornanowire growth in MOVPE. Growth of optically activeIII–V materials on silicon is important for applications com-bining optoelectronics and standard silicon electronics insmall scale devices. Previously, III–V semiconductor nano-wire growth on silicon has been demonstrated using goldnanoparticle catalysts.5 However, gold nanoparticle mediatedgrowth produces unwanted effects in silicon, such as intro-duction of deep levels6 and gold migration on the semicon-ductor surface.7 Since here gold is not required, contamina-tion is avoided.The nanowire samples were fabricated in a horizontalatmospheric pressure MOVPE reactor using trimethylindiumTMI, tertiarybutylphosphine TBP, and tertiarybutylarsineTBA precursors for indium, phosphorus, and arsenic, re-spectively. For In droplet fabrication TMI was introduced tothe reactor at 5 mol/min for 15 s at 350 °C. However, atthe extremely low temperature used here only a fraction ofthe metal organic precursors decompose. Nanowire growthwas started by introducing TBP in the reactor immediatelyafter droplet deposition. Nanowires were grown at 350 °Cfor 105 s. The reported temperatures are thermocouple read-ings and a few tens of degrees higher than the real substratesurface temperature. The samples were characterized usingscanning electron microscope SEM, transmission electronmicroscope TEM, and room-temperature photolumines-cence PL measurements.In droplets deposited in situ by MOVPE on a Si111substrate are shown in the SEM image of Fig. 1a. A topview is shown in Fig. 2a. The droplets are semispherical inshape, having an average diameter of about 80 nm and anareal density of 1.4108 cm−2. Based on measurements onthe image, the contact angle of all semispherical dropletswith the substrate surface is about 125°. InP nanowires at theedge of a Si111 substrate grown using the In droplets asaElectronic mail: marco.mattila@tkk.fibAlso at Nanomaterials Group, Laboratory of Physics and Centre for NewMaterials, Helsinki University of Technology, P.O. Box 1000, FIN-02044VTT, Finland.FIG. 1. SEM image of a In droplets and b InP nanowires at the edge ofa Si111 substrate. The inset shows a close-up image of a droplet and thecontact angle. The scale bars correspond to 1 m.APPLIED PHYSICS LETTERS 89, 063119 20060003-6951/2006/896/063119/3/$23.00 © 2006 American Institute of Physics89, 063119-1 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:130.233.216.27 On: Mon, 04 May 2015 10:02:31seeds are shown in the SEM image of Fig. 1b. A top viewof the same sample is shown in Fig. 2c. Clearly, growth hasresulted in nanowires pointing off the plane of the substrate.In addition to linear nanowires 1–2 m in length, there are anumber of curved and much shorter nanowires on the sub-strate. Curiously, no completely vertical nanowires can beobserved. The average nanowire diameter in the figure isabout 55 nm, and the average diameter of the droplet at thetip is about 90 nm.Figures 2b–2d show top-view SEM images ofsamples with InP nanowires seeded by in situ deposited Indroplets. The nominal V/III molar ratios used are 100, 200,and 300, respectively. It is clear that the tapering of the nano-wire can be controlled with the V/III ratio. A small ratioproduces reverse tapered nanowires, where the diameter islarger at the tip than at the base. Increasing the ratio reversesthe behavior. In between there is an optimal ratio here about200 where nanowire tapering is negligible. All this is iden-tical to catalyst-free growth of homoepitaxial InP nanowiresreported by Novotny and Yu.4 Also, the areal density andaverage base diameter of the straight nanowires seem to be afunction of the V/III ratio. This suggests that there are moredynamics to the droplet formation than can be deduced fromthe image of the cooled-down droplet sample in Figs. 1aand 2a. Introducing phosphorus after droplet deposition canand probably will affect the size and distribution of thedroplets.Further insight about the crystal structure of the nano-wires was acquired by transmission electron microscopy. ATEM image of a single linear InP nanowire is shown in Fig.3a. In this particular case there are no signs of stackingfaults. Figure 3b shows a high-resolution TEM image at theedge of the same nanowire. The inset shows a TEM diffrac-tion image taken perpendicularly to the nanowire axis. In-dexing the diffraction pattern reveals that the crystal struc-ture of the nanowires is wurtzite and that the nanowire axis isperpendicular to the c axis of the lattice. This is common forGaN nanowires,8 but has not been reported before for InPnanowires.It should be noted that no special precautions were takento remove the native oxide 10 Å from the substrates be-fore nanowire growth. In fact, a sample treated with hydrof-luoric acid and annealed at 800 °C under hydrogen beforethe droplet deposition exhibited no nanowire growth.This result is in contrast with results reported byMårtensson et al.5 on III–V semiconductor nanowire growthon silicon using gold nanoparticle catalysts. However, in ourexperiments here the native oxide alone was not enough toinduce nanowire growth, since no nanowires were observedin samples where the droplet deposition step had been omit-ted. Also, no growth was observed on a 300 nm thick SiO2layer grown on silicon by plasma-enhanced chemical vapordeposition. This suggests that the In droplets actually pen-etrate the native oxide and that the nanowires start growingfrom the silicon-indium interface. Further studies are re-quired to find out also whether catalyst-free nanowire growthon oxide-free silicon is possible using different growth pa-rameters.Room-temperature PL spectra measured from InAsPnanowires detached from the substrate are shown in Fig. 4.The nominal TBP/III molar ratio was 200, and the nominalTBA/V molar ratio in the gas phase during growth is notednext to the spectra. Adding a small amount of TBA to the gasphase had no significant effect on the morphology of thenanowire samples SEM images not shown. InP wires ex-hibit a luminescence peak at 1.35 eV spectrum i whichequals the energy gap of zinc-blende InP. This is in contrastwith the TEM results. Previously, we and other groups haveproposed that the wurtzite modification in InP nanowiresleads to a blueshift of the photoluminescence peak energy.9,10However, in these cases the growth direction of the nano-wires has been along the c axis of the wurtzite structure.Further studies are required to find out whether here the lackof this blueshift is due to the different orientations of thenanowires with respect to the crystal axes, which could leadto different strain or surface effects. Since the nanowire di-ameter is larger than the exciton Bohr radius in bulk InP20 nm, no blueshift from quantum confinement is ex-pected. The spectra iii, iv, and v in Fig. 4 also exhibitluminescence peaks at 1.18, 1.10, and 1.03 eV, respectively.We assume that these peaks originate from InAsxP1−x. Thesurprising result here is that the PL peak corresponding tobulk InP is present alongside the peak of InAsP. One expla-FIG. 2. SEM image of a a Si111 surface with in situ deposited In drop-lets, b InP nanowires grown on Si111 with a V/III ratio of 100, c V/IIIratio of 200, and d V/III ratio of 300. The scale bar corresponds to 1 m.FIG. 3. a TEM image of a linear InP nanowire. The inset shows a close-upof the droplet-nanowire interface. b High-resolution TEM image of thesame wire. The inset shows an electron diffraction pattern taken perpendicu-larly to the nanowire axis.063119-2 Mattila et al. Appl. Phys. Lett. 89, 063119 2006 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:130.233.216.27 On: Mon, 04 May 2015 10:02:31nation to this behavior is that the nanowires are actually so-called core-shell structures11 having an InAsP core under anInP shell because the samples are cooled down in a phos-phoric ambient. Compositional fluctuations in the axial di-rection are also possible. It can be seen from the spectra thatas the As content is increased the PL intensity of the InAsPInP related peak increases decreases. This can be under-stood as a result of more localized carriers in the InAsP partswith increasing As content and thus supports the existence ofcompositional fluctuations. For more compositional informa-tion, energy dispersive x-ray EDX analysis was conductedon one of the samples EDX spectra not shown. The resultsconfirmed that there are only segments of InAsP in otherwisepure InP nanowires, and thus support compositional fluctua-tions in the axial direction. We believe that this is the case inall samples where a bimodal PL signal is observed. However,when As content in the gas phase is further increased, no PLsignal from InP is observed anymore spectrum vi inFig. 4. No PL signal from InAsP is observed either, althoughit is possible that the emission of the As-rich nanowires fallsoutside the range of the germanium detector.In summary, catalyst-free growth of InAsP nanowireson Si111 substrates was demonstrated. In droplets depos-ited in situ by MOVPE were used as seeds for off-substratenanowire growth. The native oxide on the substrates wasfound to have a crucial role in the formation of the nano-wires. No nanowire growth was observed on silicon withoutthe native oxide or on a thick SiO2 layer. The InP nanowiresexhibited wurtzite crystal structure and room-temperaturephotoluminescence at 1.35 eV. The nanowire axis was foundto be perpendicular to the c axis of the wurtzite crystal. Al-loying the nanowires with As produced under certain condi-tions a bimodal spectrum exhibiting a PL peak at the energyof InAsP in addition to a peak corresponding to the energygap of InP.1X. Duan, Y. Huang, Y. Cui, J. Wang, and C. M. Lieber, Nature London409, 66 2001.2R. S. Wagner and W. C. Ellis, Appl. Phys. Lett. 4, 89 1964.3W. Seifert, M. Borgström, K. Deppert, K. A. Dick, J. Johansson, M. W.Larsson, T. Mårtensson, N. Sköld, C. P. T. Svensson, B. A. Wacaser, L. R.Wallenberg, and L. Samuelson, J. Cryst. Growth 272, 211 2004.4C. J. Novotny and P. K. L. Yu, Appl. Phys. Lett. 87, 203111 2005.5T. Mårtensson, C. P. T. Svensson, B. A. Wacaser, M. W. Larsson, W.Seifert, K. Deppert, A. Gustafsson, L. R. Wallenberg, and L. Samuelson,Nano Lett. 4, 1987 2004.6C. B. Collins, R. O. Carlson, and C. J. Gallagher, Phys. Rev. 105, 11681957.7J. B. Hannon, S. Kodambaka, F. M. Ross, and R. M. Tromp, NatureLondon 440, 69 2006.8X. Duan and C. M. Lieber, J. Am. Chem. Soc. 122, 188 2000.9M. Mattila, T. Hakkarainen, M. Mulot, and H. Lipsanen, Nanotechnology17, 1580 2006.10J. Motohisa, J. Noborisaka, J. Takeda, M. Inari, and F. Fukui, J. Cryst.Growth 272, 180 2004.11L. J. Lauhon, M. S. Gudiksen, D. Wang, and C. M. Lieber, NatureLondon 420, 57 2002.FIG. 4. Room-temperature photoluminescence spectra of InAsP nanowiresdetached from the substrate. The dashed line is a guide for the eyes.063119-3 Mattila et al. Appl. Phys. Lett. 89, 063119 2006 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:130.233.216.27 On: Mon, 04 May 2015 10:02:31

Catalyst-free growth of In(As)P nanowires on silicon

The catalyst-free metal organic vapor phase epitaxial growth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowire growth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InP nanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies

Lipsanen, H.

Jiang, Hua

VTT Research System

https://aaltodoc.aalto.fi/bitstream/handle/123456789/15868/A1_mattila_m_2006.pdf?sequence=1&isAllowed=y

Catalyst-free growth of In(As)P nanowires on silicon

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