A Radio Frequency Single-Electron Transistor Based on an InAs/InP Heterostructure Nanowire Henrik A. Nilsson,* ,† Tim Duty, | Simon Abay, § Chris Wilson, § Jakob B. Wagner, ‡ Claes Thelander, † Per Delsing, § and Lars Samuelson † Solid State Physics, Lund UniVersity, Box 118, S-221 00, Lund, Sweden, Microtechnology and Nanoscience, Chalmers UniVersity of Technology, S-412 96, Göteborg, Sweden, School of Physical Sciences, The UniVersity of Queensland, St. Lucia, 4072 Australia, and Polymer and Materials Chemistry/nCHREM, Lund UniVersity, Box 124, S-221 00, Lund, Sweden Received November 28, 2007; Revised Manuscript Received January 23, 2008 ABSTRACT We demonstrate radio frequency single-electron transistors fabricated from epitaxially grown InAs/InP heterostructure nanowires. Two sets of double-barrier wires with different barrier thicknesses were grown. The wires were suspended 15 nm above a metal gate electrode. Electrical measurements on a high-resistance nanowire showed regularly spaced Coulomb oscillations at a gate voltage from -0.5 to at least 1.8 V. The charge sensitivity was measured to 32 μe rms Hz -1/2 at 1.5 K. A low-resistance single-electron transistor showed regularly spaced oscillations only in a small gate-voltage region just before carrier depletion. This device had a charge sensitivity of 2.5 μe rms Hz -1/2 . At low frequencies this device showed a typical 1/f noise behavior, with a level extrapolated to 300 μe rms Hz -1/2 at 10 Hz. Single-electron transistors 1 (SETs) are extremely sensitive electrometers. In the so-called RF-SET 2 the dissipation in the SET is measured using radio frequency (rf) reflectometry which extends the operation frequency by several orders of magnitude to well above 10 MHz. This has allowed operation at frequencies above the 1/f noise corner, 3 which has resulted in very high sensitivities. 4,5 Even higher frequencies can be reached by using the RF-SET as a mixer. 6,7 The combination of high speed and very high charge sensitivity has made it possible to study a wide range of physical phenomena such as nanomechanical oscillators, 8,9 charge fluctuators, 10–12 discrete electron transport, 13–15 and qubit readout. 16–18 So far most RF-SETs have been using Al/AlO x /Al tunnel junctions; however, SETs based on GaAs quantum dots 10,15 and carbon nanotubes 19 have also been used in the rf mode. Recent technological developments have allowed us to fabricate a new type of SET based on epitaxially grown InAs/ InP heterostructure nanowires. 20,21 The difference in band gap between InAs and InP can be used to form tunnel barriers, and the SET structure can be grown vertically in the nanowire. These nanowire SETs have several unique properties which may offer enhanced electrometer perfor- mance. First, the charging energy of the nanowire SETs can be very high, since the size of the middle island between the two tunnel barriers can be defined by epitaxial growth. Second, the very high quality of the heterostructure interfaces results in very uniform and epitaxial tunnel barriers. Another interesting property is that the nanowire SETs can easily be suspended above a substrate. In this paper we present the first demonstration of a nanowire SET operated in the rf mode. We demonstrate operation at 1.5 K, and we obtain a charge sensitivity close to that of the best aluminum RF-SETs. 4 In addition we present low-frequency noise measurements of this nanowire RF-SET. Two batches of InAs/InP nanowires with diameters of 50–60 nm were grown by chemical beam epitaxy from Au aerosol nanoparticles. 22,23 In the middle of the 2–3 μm long InAs wires, two InP barriers were grown. In the first batch of wires the barriers were grown approximately 4–5 nm thick with a spacing of 150 nm. This double-barrier structure is shown in Figure 1a. In the second batch, the barriers were grown thinner, 2–3 nm, with a spacing of 50 nm. The two batches of wires will be referred to as the high resistance (first batch) and the low resistance wires (second batch). To measure the nanowires, metal stripe structures were made by electron beam lithography and Ti/Au evaporation/ lift-off on low-doped Si substrates that were capped with * Corresponding author. E-mail: henrik.nilsson@ftf.lth.se. † Solid State Physics, Lund University. ‡ Polymer and Materials Chemistry/nCHREM, Lund University. § Microtechnology and Nanoscience, Chalmers University of Technology. | School of Physical Sciences, The University of Queensland. NANO LETTERS 2008 Vol. 8, No. 3 872-875 10.1021/nl0731062 CCC: $40.75  2008 American Chemical Society Published on Web 02/27/2008