Contains table of contents for Section 2, research goals and objectives, summary of recent work and a list of publications.Joint Services Electronics Program Grant DAAL04-95-1-0038U.S. Army Research Office Grant DAAH04-94-G-011

Abusch-Magder, David

Goldhaber-Gordon, David J.

Kastner, Marc A.

Lyszczarz, Theodore M.

Mankiewich, Paul M.

Morgan, Nicole Y.

Shaver, David C.

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Section 2 Quantum-Effect DevicesChapter 1 Single-Electron ElectronicsChapter 2 Theory of Coulomb Blockade in SemiconductorDevices .Chapter 3 Superconducting and Quantum-Effect ElectronicsChapter 4 Nanostructures Technology, Research, andApplicationsChapter 5 Single-Electron Spectroscopy4950 RLE Progress Report Number 139Chapter 1. Single-Electron ElectronicsChapter 1. Single-Electron ElectronicsAcademic and Research StaffProfessor Marc A. KastnerVisiting Scientists and Research AffiliatesTheodore M. Lyszczarz, 1 Paul M. Mankiewich, 2 David C. Shaver1Graduate StudentsDavid Abusch-Magder, David J. Goldhaber-Gordon, Nicole Y. Morgan1.1 Goals and ObjectivesSponsorsJoint Services Electronics ProgramGrant DAAL04-95-1-0038U.S. Army Research OfficeGrant DAAH04-94-G-0119When electrons are confined to a small particle ofmetal or a small region of a semiconductor, boththe energy and charge of the system are quantized.In this way, such nanometer-sized systems behavelike artificial atoms.3 The quantization of energy isfamiliar: the solutions of the Schr6dinger equationin an isolated region have discrete energies. Insome ways, however, the quantization of charge ismore mysterious. We are quite comfortable withthe idea that the charge of a collection of electronsis discrete. However, the charge in any smallvolume of a large sample of a conductor is not dis-crete because the electronic wave functions areextended over the entire sample. Only when thestates are localized is the charge quantized.Artificial atoms have been constructed using metalsand semiconductors; and they have been given avariety of names: single-electron transistor (SET),quantum dot, and zero-dimensional electron gas.The physics of these devices is the same, althoughthe limits in which they operate may be quite dif-ferent. The goal of our research is to better under-stand the physics of these devices in order tooptimize their performance so that circuit designcan begin.1.2 Summary of Recent WorkWe have recently fabricated metal-oxide-siliconsingle-electron transistors (MOSSETs) which showsingle-electron phenomena up to 20 K. A single-electron transistor (SET) is an island of chargewhich is coupled to leads by tunnel barriers. Thereare two energies that are encountered in changingthe electronic state of the SET: (1) the energyrequired to add an electron to the island, U, and (2)the energy required to excite the electrons alreadyon the island, AE. Both of these energies increaseas the size of the island is diminished. Since theresolution of single-electron phenomena is limitedby the temperature of the electrons, we canincrease the operating temperature by reducing thesize of the SET. The purpose of our work is to fab-ricate small SETs and, in addition to achievinghigher operating temperatures, to exploit theimproved relative resolution to explore coherentinteraction between the electrons in the leads andthe electrons on the island.An island of charge can be created by electrostaticdepletion of a two-dimensional electron gas(2DEG). By changing the voltages on metallicgates which lie a short distance above a 2DEG, theelectrostatic fields can be adjusted; in this way,both the number of electrons on the island and thesize of the tunnel barriers can be varied. The sizeof the island is limited by the depletion width, whichdecreases as the gates are brought closer to the2DEG; a small depletion width allows the possibility1 MIT Lincoln Laboratory, Lexington, Massachusetts.2 AT&T Bell Laboratories, Short Hills, New Jersey.3 M.A. Kastner, "Artificial Atoms," Phys. Today 46(1): January 24 (1993).Chapter 1. Single-Electron Electronicsof a small island. Thus, to make small SETs oneneeds a material system in which the gates can bebrought close to the 2DEG. The Si-SiO2 MOSsystem is ideal for this purpose because SiO2 is arobust insulator; layers as thin as 10 nm have lowleakages, high breakdown voltages, and are easilyfabricated. We have therefore chosen to fabricateSETs in the silicon MOS system, rather than in themore extensively studied GaAs-AIGaAs system.Previously observed Coulomb blockade (CB) effectsin electrostatically patterned MOS structures haveresulted from impurities. More recent work 4 hasachieved CB in a Si-SiO2 system using pattern-dependent oxidation. However, our studies werethe first to show well-defined CB phenomena inlithographically defined MOSSETs where the tunnelbarriers are created by gate electrodes.Standard silicon fabrication techniques have beenused in combination with electron-beam lithographyto fabricate MOSSETs, thus taking advantage ofexisting technology. We have observed periodicconductance oscillations resulting from CB in aMOSSET, with an addition energy U = 15 meV,which corresponds to temperature T = U/kB=175 K.However, the widely spaced peaks correspondingto these large energies are usually modulated bywhat appears to be CB peaks with a smaller period.Lack of reproducibility of this fine structure suggeststhat it results from disorder at the Si/SiO2 interface.We believe that these effects of disorder may becontrolled by improvement of the interface. Ourmobilities are much lower than those that havebeen obtained elsewhere, so less disordered inter-faces are possible. However, our studies mayprovide a useful new probe of the nature of disorderat the Si/SiOz interface, which might be technolog-ically valuable.1.3 PublicationsAbusch-Magder, D.M., M.A. Kastner, C.L. Dennis,W.F. Dinatale, T.M. Lyszczarz, D.C. Shaver, andP.M. Mankiewich. "Coulomb Blockade in aSilicon Mosset." Conference Proceedings of theNATO Advanced Study Institute on QuantumTransport in Semiconductor Submicron Struc-tures, 1996.Kastner, M.A. "Artificial Atoms: Their Physics andPotential Application." FED J. 7: 3 (1996).Kastner, M.A. "Mesoscopic Physics with ArtificialAtoms." Comm. Condensed Matter Phys. 17:349 (1996).Kastner, M.A. "Mesoscopic Physics with ArtificialAtoms." Proceedings of the 23rd InternationalConference on the Physics of Semiconductors1: 27 (1996).Klein, O., D.J. Goldhaber-Gordon, C. de C.Chamon, and M.A. Kastner. "Magnetic-fieldDependence of the Level Spacing of a SmallElectron Droplet." Phys. Rev. B. 53: R4221(1996).Klein, O., C. de C. Chamon, D. Goldhaber-Gordon,M.A. Kastner, and X.G. Wen. "Phase Transi-tions in Artificial Atoms." Conference Pro-ceedings of the NA TO Advanced Study Instituteon Quantum Transport in Semiconductor Sub-micron Structures, 1996.Klein, O., C. de C. Chamon, D. Tang, D.M. Abusch-Magder, U. Meirav, X.-G. Wen, and M.A.Kastner. "Study of a Coulomb Island in StrongMagnetic Fields." Proceedings of the 11th Inter-national Conference on High Magnetic Fields inSemiconductors. Singapore: World Scientific,1996, p. 472.4 Y. Takahashi, M. Nagase, H. Namatsu, K. Kurihara, K. Iwadate, Y. Nakajima, S. Horiguchi, K. Murase, and M. Tabe, "FabricationTechnique for Si Single-Electron Transistor Operating at Room Temperature," Electron. Lett. 31: 136 (1995).52 RLE Progress Report Number 139

Single-Electron Electronics

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Single-Electron Electronics

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