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Charge detection in semiconductor nanostructures

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dc.contributor.advisor Marc A. Kastner. en_US MacLean, Kenneth (Kenneth MacLean, III) en_US
dc.contributor.other Massachusetts Institute of Technology. Dept. of Physics. en_US 2011-05-23T18:02:48Z 2011-05-23T18:02:48Z 2010 en_US 2010 en_US
dc.description Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010. en_US
dc.description Cataloged from PDF version of thesis. en_US
dc.description Includes bibliographical references (p. 137-145). en_US
dc.description.abstract In this thesis nanometer scale charge sensors are used to study charge transport in two solid state systems: Lateral GaAs quantum dots and hydrogenated amorphous silicon (a-Si:H). In both of these experiments we use time-resolved charge sensing to study electron transport in regimes that are not accessible to traditional transport measurements. For the lateral GaAs quantum dot experiments, we use a GaAs quantum point contact integrated with the dot as a charge sensor. We use this sensor to observe single electrons hopping on and off the dot in real time. By measuring the time intervals for which the dot contains one and zero electrons, we probe the rate F at which electrons tunnel on and off the dot from the leads. We measure F as a function of the drain source bias V, and gate voltages V applied to the dot. At zero magnetic field, we show that the dependencies of F on Vda and V can be understood in terms of a simple quantum mechanical model which takes into account variations in the electron energy relative to the top of the tunnel barriers separating the dot from the leads. We also show that the tunneling is dominated by elastic processes. At high magnetic fields, we show that tunneling into the excited spin state of the dot can be completely suppressed relative to tunneling into the ground spin state. The extent of the suppression depends on the shape of the electrostatic potential defining the quantum dot. For the a-Si:H experiments, we pattern a nanometer scale strip of a-Si:H adjacent to a narrow silicon MOSFET (metal-oxide-semiconductor field-effect transistor), which serves as an integrated charge sensor. We show that the MOSFET can be used to detect charging of the a-Si:H strip. By performing time-resolved measurements of this charging, we are able to measure extremely high resistances (~ 1017 Q) for the a-Si:H strip at T ~ 100 K. At higher temperatures, where the resistance of the a-Si:H strip is not too large, we show that the resistances obtained from our charge detection method agree with those obtained by measuring current. Our device geometry allows us to probe a variety of electron transport phenomena for the a-Si:H, including the field effect and dispersive transport, using charge detection. We extract the density of localized states at the Fermi level for the a-Si:H and obtain consistent results. We discuss the effect of screening by the substrate on the sensitivity of the MOSFET to charge in the a-Si:H, and show that the MOSFET can detect switching noise in the a-Si:H. en_US
dc.description.statementofresponsibility by Kenneth MacLean. en_US
dc.format.extent 145 p. en_US
dc.language.iso eng en_US
dc.publisher Massachusetts Institute of Technology en_US
dc.rights M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. en_US
dc.rights.uri en_US
dc.subject Physics. en_US
dc.title Charge detection in semiconductor nanostructures en_US
dc.type Thesis en_US Ph.D. en_US
dc.contributor.department Massachusetts Institute of Technology. Dept. of Physics. en_US
dc.identifier.oclc 720922497 en_US

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