Silvano De Franceschi Laboratorio Nazionale TASC INFM-CNR, Trieste, Italy  Nanowire growth and properties  Integration with Si technology  Manipulation and NEMS  Single electron transport  Gate-controlled proximity supercurrent Outline

gold particle liquid Au-InP eutect vapor nanowire time Catalytic (VLS) crystal growth Semiconductor nanowires Key features: nanoscale diameter (few to 100 nm) High aspect ratio (1-100 micron long) Versatility in composition

heterojunctions p-n junctions hollow Possible nanowire structures coaxial

10 nm InP wire on SiO 2 [111] Zinc Blende [111] direction Before growth

Bakkers et al., JACS 2003, 125, 3440 Hollow core wall 5 nm wall Zinc Blende crystal structure 200 nm InP Tubes

50 nm Coaxial wires Group III modulation Position (nm) Counts Ga P In InP GaP

Heterojunctions Group V modulation GaAs GaP GaAs Au 100 nm GaP: 1.8 nm/sec GaAs: 5.0 nm/sec

Björk et al., NanoLetters 2, 87 (2002) InAs InP InAs Almost atomically sharp interfaces No strain-induced dislocations (stress can relax at the surface) (001) Heterostructures nanowires (Samuelson’s group – Lund) (Chemical beam epitaxy, MOVPE)

Epitaxial InP wires on Ge 5  m InP Ge I The InP/Ge heterointerface provides a low-resistance Ohmic contact between wire and substrate HR TEM Conducting AFM More recently: epitaxial InP on Si!  Integration of III-V devices with Si technology [See also Mårtensson et al., Nano Letters 4, 1987 (2004)] V sd (mV) I (mV)

Silicon Gate Source Drain III-V Vertical transistor Silicon Source Drain p n Nano LED III-V devices on silicon NANOWIRE LED: Gudiksen et al., Nature (2002) NANOWIRE LASERS: Johnson et al., Nature Materials (2002) Duan et al., Nature (2003) Enhanced speed Enhanced transconductance Small footprint

More on Nanowire devices… Law et al., Science 305, 1269 (2004). Nanowire optical waveguides Dick et al., Nature Materials 3, 380 (2004). Nanowire trees Cui et al., Science 293, 1289 (2001). Nanowire biosensors

AFM manipulation

Electrically-driven nanowire cantilever Nanowire “string”

After wet etching… following subsequent AFM manipulation….

V s-d V gate SiO 2 Si p+ Device fabrication: -wires deposited on p-type Si wafer with a 250-nm-thick surface oxide -Ti/Al contacts defined by e- beam lithography Low-temperature transport in semiconductor NWs InP & InAs n-type nanowires Diameter: 25 – 140 nm Length: 2 – 20  m

Single-electron tunneling in InP nanowires V SD [mV] V gate [mV] L~600 nm T~350 mK E c ~1 meV Differential conductance (black: low, white: high); Many diamonds visible. Not so regular, but very stable and reproducible. Single & Multiple(probably two)-island behavior Typical island size: ~100 nm

B = 31 mT B = 0.5 T V (  V) V g (mV) gBBgBB g = 1.5 ± 0.2 InP-nanowire quantum dot: Zeeman spin splitting EE N N+1

Tunable Quantum Dots top gates source drain Side gates Few-electron quantum dots in InAs/InP nanowires Björk et al., Nano Lett. 4, 1621 (2004) InAs QD InP barriers

S S N (1-D or 0-D) Kasumov et al, Science 284 (’99) Morpurgo et al., Science 286 (’99) Buitelaar et al., PRL 89 (’02); PRL 91 (‘03) Jarillo-Herrero et al. (unpublished) Superconductor Nanowire Superconductor For T < 1.2 K Only a few experiments done on similar hybrid systems based on carbon nanotubes: Superconducting contacts => Proximity effect Low contact resistance => no Coulomb blockade

InAs nanowire devices Ti(10 nm)/Al(120 nm) L sd = 60 – 500 nm V gate SiO 2 Si (p+) 4-point contacts: InAs [100]  L sd W source drain Device resistances: 0.4 – 4 K 

Supercurrent in InAs nanowires T = 40 mK I C = 136 nA R N = 417  I C R N = 60  V ~  0 /e Hysteretic behavior due to strong capacitive coupling between source and drain (90 % device yield!) Enhanced conductance for 2  0 <V<2  0  High contact transparency (T~75%)  B=0 20/e20/e

Multiple Andreev reflection From 3 different devices: Peaks at V n =2  0 /ne: V 1 =2  0 /e V 2 = 2  0 /2e V 3 = 2  0 /3e Normal Super    N S  T < Tc Andreev reflection in a S-N junction

Field-effect control of the supercurrent Supercurrent fluctuations correlate with normal-state universal conductance fluctations 0 30 k  Electron transport through the nanowire is diffusive and phase coherent => mesoscopic Josephson junctions First Josephson Field Effect Transistors: Takayanagi et al., PRL (1985). Kleinsasser et al., Appl. Phys. Lett. (1989). Nguyen et al., Appl. Phys. Lett. (1990).

 V=10  V  V= (  /2e)  rf =  V for 1 GHz “Quantized voltage steps depending on RF frequency” AC Josephson effect: Rf irradiation => Shapiro steps

Shapiro steps: rf-power dependence  rf = 2 GHz  rf = 4 GHz  rf = 5 GHz  I N ~ N-th order Bessel function with I C,fit = 34 nA > I C,exp = 26 nA ICIC  I N=1  I N=2  I N=3  I N=4 (a) (b)(c)

Gate-controlled SQUID

Jorden van Dam Floris Zwanenburg L. Gurevich Yong-Joo Doh Leo Kouwenhoven Erik Bakkers Aarnoud Roest Lou-Fe Feiner Philips Eindhoven: Epitaxial III-V nanowires on Ge [Nature Materials 3, 769 (2004)] Nanowire SET [Appl. Phys. Lett. 83, 344 (2003)] Nanowire JOFET [Science 309, 272 (2005)] Nanowire SQUID [unpublished] References Collaborators