Contains a description on one research project.Joint Services Electronics Program DAAL03-89-C-000

Antoniadis, Dimitri A.

Field, Stuart B.

Heiblum, Mordehai

Kastner, Marc A.

Meirav, Udi

Odoardi, Angela R.

Park, Samuel L.

Scott-Thomas, John H. F.

Smith, Henry I.

Wind, Shalom

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Chapter 4. Ultralow Temperature StudiesChapter 4. Ultralow Temperature Studies ofNanometer Size Semiconductor DevicesAcademic and Research StaffProfessor Marc A. Kastner, Professor Dimitri A. Antoniadis, Dr. Stuart B. Field, Professor HenryI. SmithVisiting Scientists and Research AffiliatesMordehai Heiblum,' Shalom Wind'Graduate StudentsUdi Meirav, Samuel L. Park, John H.F. Scott-ThomasTechnical and Support StaffAngela R. Odoardi4.1 Project DescriptionSponsorJoint Services Electronics ProgramContract DAAL03-89-C-0001In the late 1970s, the rapidly improving the-oretical description of disordered metalscombined with the rapidly evolving tech-nology of submicron lithography to create anew subfield of condensed-matter physics.The electronic properties of artificial struc-tures - which are large compared withatomic size scales but comparable toquantum mechanical coherence lengths -have been shown to be fundamentally dif-ferent from both those of larger and smallerstructures. For this reason, the term"mesoscopic" was coined to differentiatethem.Almost from the start, the hallmark ofmesoscopic structures has been the random,noise-like, but reproducible fluctuations intheir conductance. These fluctuations werefirst seen in the insulating regime of one-dimensional field-effect transistors whentheir Fermi energy was varied. The most dra-matic discovery was that, in metallic samples,independent of their size and geometry, thefluctuations had magnitude of order e2/h inthe limit of zero temperature. These Uni-versal Conductance Fluctuations were seenwhen the magnetic field, Fermi energy, orimpurity configuration was varied, consistentwith the theory of Altshuler, Lee and Stone.2Recently, we reported the discovery of a newphenomenon in mesoscopic field effectstructures. In the same regime where expo-nentially large random fluctuations had beenseen in earlier devices,2 we found fluctu-ations which, while still exponentially large,were accurately periodic in the density of theelectron gas. We were the first to observethese oscillations in Si MOSFETs 3 fabricatedat MIT and in novel GaAs invertedsemiconductor-insulator-semiconductor field1 IBM Thomas J. Watson Research Laboratories.2 For a review see M. A. Kastner, R. F. Kwasnick, J. C. Licini, and D. J. Bishop, "Conductance Fluctuations near theLocalized-to-Extended Transition in Narrow Si MOSFETs," Phys. Rev. B 36: 8015 (1987).3 J.F.H. Scott-Thomas, M.A. Kastner, D.A. Antoniadis, H.I. Smith, and S.B. Field, "Si Metal-Oxide SemiconductorField Effect Transistor with 70-nm Slotted Gates for Study of Quasi-One-Dimensional Quantum Transport," J.Vac. Sci. Technology B 6: 1841 (1988); J.F.H. Scott-Thomas, S.B. Field, M.A. Kastner, H.I. Smith, and D.A.121Chapter 4. Ultralow Temperature Studieseffect transistors ISIS structures fabricated atIBM. 4 An example of the latter is shown infigure 1.A rich phenomenology is associated with thisoscillatory behavior. The conductance isthermally activated between 1 K and about0.3 K, and the activation energy oscillateswith the number of electrons per unit length.At a lower temperature there is a tunnelingcomponent which also oscillates. The con-ductance is highly non-ohmic, showing dra-matic threshold behavior with thresholdvoltage that oscillates out of phase with theconductance. Most surprising of all, theoscillations are independent of magneticfield. This is probably why the phenomenonwas not observed earlier by other groups thattypically study MODFETs in which the carrierdensity can not be varied over a wide range.For the quantum Hall effect, the variation ofcarrier density is equivalent to the variationof magnetic field. This is not the case for ournew phenomenon.The phenomenology suggests that the oscil-lations result from the opening of an energygap whenever an integral number of elec-trons resides in a subsection of the one-dimensional channel. Several models havebeen proposed to explain the observations.It is probable that the electron-electron inter-actions are crucial. If so, this will be the firsttime that many-body effects will have beenshown to dominate the behavior ofmesoscopic systems.The silicon deviceGaAs fabricationNational Sciencefabrication and part of thewas sponsored by theFoundation under GrantECS 88-13250. A portion of the ultralowtemperature measurements was sponsored bythe Joint Services Electronics Program underContract DAAL03-89-C-0001.2.01.5x0100.5 0 (a)535 545 555 565Vg (mV)a- (b)o0 200 400 600 800 1000Frequency 1/v 9 (V 1)Figure 1. (a) Conductance vs. gate voltage of anarrow channel, 2 pm long, measured at T = 50 mK.The inset shows an expansion of the first few oscil-lations. (b) Fourier power spectrum of the above. Thepeak corresponds to a period of AVa1.7 mV.Antoniadis, "Conductance Oscillations Periodic in the Density of a One-Dimensional Electron Gas," Phys. Rev.Lett. 62: 583 (1989).4 U. Meirav, M.A. Kastner, M. Heiblum, and S.J. Wind, "A One-Dimensional Electron Gas in GaAs: PeriodicConductance-Oscillations as a Function of Density," Phys. Rev. (Rapid Comm.) B 40: 5871 (1989); U. Meirav,M. Heiblum, and F. Stern, Appl. Phys. Lett. 52: 1268 (1988).122 RLE Progress Report Number 132

Ultralow Temperature Studies of Nanometer Size Semiconductor Devices

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Ultralow Temperature Studies of Nanometer Size Semiconductor Devices

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