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Dive into the research topics where D. C. Driscoll is active.

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Featured researches published by D. C. Driscoll.


Physical Review Letters | 2006

Counting statistics of single electron transport in a quantum dot.

Simon Gustavsson; R. Leturcq; B. Simovič; R. Schleser; Thomas Ihn; P. Studerus; Klaus Ensslin; D. C. Driscoll; A. C. Gossard

We have measured the full counting statistics of current fluctuations in a semiconductor quantum dot (QD) by real-time detection of single electron tunneling with a quantum point contact. This method gives direct access to the distribution function of current fluctuations. Suppression of the second moment (related to the shot noise) and the third moment (related to the asymmetry of the distribution) in a tunable semiconductor QD is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels.


Applied Physics Letters | 2004

ErAs:GaAs photomixer with two-decade tunability and 12μW peak output power

J. E. Bjarnason; T. L. J. Chan; A. W. M. Lee; E. R. Brown; D. C. Driscoll; M. Hanson; A. C. Gossard; Richard E. Muller

This letter reports the fabrication and demonstration of an ErAs:GaAs interdigitated photomixer as a tunable THz source ranging from ∼20GHzto∼2THz, with 12μW maximum power typically around ∼90GHz. Each photomixer is coupled to a composite dipole-spiral planar antenna that emits a Gaussian-type beam into free space. The beam switches from dipole to spiral antenna behavior as the frequency increases. A distributed Bragg reflector is embedded in the device beneath the photomixer to increase its external quantum efficiency. The photomixer has a 900A thick silicon nitride coating which serves as an antireflection and passivation layer, and also improves the reliability and heat tolerance of the device.


Applied Physics Letters | 2003

Photomixing and photoconductor measurements on ErAs/InGaAs at 1.55 μm

M. Sukhotin; E. R. Brown; A. C. Gossard; D. C. Driscoll; M. Hanson; Paul D. Maker; Richard E. Muller

We report here the fabrication and demonstration of the photomixers made from In0.53Ga0.47As epitaxial material lattice-matched to InP. The material consists of layers of ErAs nanoparticles separated by InGaAs and compensated with Be to reduce the photocarrier lifetime to picosecond levels and to increase the resistivity to ∼100 Ω cm. Interdigitated-electrode and planar-antenna structures were fabricated by e-beam lithography and tested for dc electrical characteristics, 1.55-μm optical responsivity, and difference-frequency photomixing. The measured responsivity of 8 mA/W and photomixer output of >0.1 μW beyond 100 GHz are already comparable to GaAs photomixers and suggest that coherent THz generation is now feasible using the abundant 1.55-μm-semiconductor-laser and optical-fiber technologies.


Applied Physics Letters | 2001

Electronic structure and conduction in a metal–semiconductor digital composite: ErAs:InGaAs

D. C. Driscoll; M. Hanson; C. Kadow; A. C. Gossard

We have grown epitaxial superlattice structures of layers of semimetallic ErAs particles embedded in an InGaAs matrix on (001) Fe-doped InP substrates. Temperature-dependent Hall measurements, x-ray diffraction, and transmission electron microscopy were performed on the materials. The carrier mobility and the temperature dependence of the charge density imply conduction in the InGaAs matrix. We calculate an offset between the conduction-band minimum of the InGaAs matrix and the Fermi level of the ErAs particles that is strongly dependent on the amount of ErAs deposited. As the size of the ErAs particles increases, the Fermi level decreases from ∼0.01 eV above the InGaAs conduction-band edge to ∼0.2 eV below the InGaAs conduction-band edge and the electrical conduction properties change from metallic to semiconducting.


Applied Physics Letters | 2005

Ultrafast photoresponse at 1.55 μm in InGaAs with embedded semimetallic ErAs nanoparticles

D. C. Driscoll; M. Hanson; A. C. Gossard; E. R. Brown

We have grown epitaxial metal/semiconductor superlattice materials by molecular beam epitaxy that exhibit subpicosecond photocarrier lifetimes at 1.55 μm. The superlattice samples consist of layers of semimetallic ErAs nanoparticles embedded in a semiconducting In0.53Ga0.47As matrix. Time-resolved optical measurements are performed using a fiber-based transmission pump-probe technique with an erbium-doped-fiber mode-locked laser. Photocarrier lifetimes decrease with increasing ErAs deposition and decreasing spacing between the ErAs layers. Further reduction in the lifetime is achieved by selective beryllium doping of the superlattice; measured lifetimes ⩽0.3ps were achieved in optimized structures.


Applied Physics Letters | 2004

Time-resolved detection of individual electrons in a quantum dot

R. Schleser; E. Ruh; Thomas Ihn; Klaus Ensslin; D. C. Driscoll; A. C. Gossard

We present measurements on a quantum dot and a nearby, capacitively coupled, quantum point contact used as a charge detector. With the dot being weakly coupled to only a single reservoir, the transfer of individual electrons onto and off the dot can be observed in real time in the current signal from the quantum point contact. From these time-dependent traces, the quantum mechanical coupling between dot and reservoir can be extracted quantitatively. A similar analysis allows the determination of the occupation probability of the dot states.


Semiconductor Science and Technology | 2005

THz-photomixer based on quasi-ballistic transport

G. H. Döhler; F. Renner; O Klar; M. Eckardt; A Schwanhäußer; S. Malzer; D. C. Driscoll; M. Hanson; A. C. Gossard; G. Loata; Torsten Löffler; Hartmut G. Roskos

We report on a novel concept for THz photomixers with high conversion efficiency up to several THz. In contrast to the conventional pin photomixer we can overcome the trade-off between either optimizing transit-time or RC-roll-off. Using quasi-ballistic transport in nano-pin-diodes the transport path can be optimized regarding both path length and transit time. Independently, the capacitance can be kept small by using a sufficiently large number of optimized nano-pin-diodes in series. The concept is presented in detail and first experimental results are reported which corroborate our theoretical expectations.


Surface Science Reports | 2009

Electron counting in quantum dots

Simon Gustavsson; R. Leturcq; M. Studer; Ivan Shorubalko; Thomas Ihn; Klaus Ensslin; D. C. Driscoll; A. C. Gossard

Abstract We use time-resolved charge detection techniques to investigate single-electron tunneling in semiconductor quantum dots. The ability to detect individual charges in real-time makes it possible to count electrons one-by-one as they pass through the structure. The setup can thus be used as a high-precision current meter for measuring ultra-low currents, with resolution several orders of magnitude better than that of conventional current meters. In addition to measuring the average current, the counting procedure also makes it possible to investigate correlations between charge carriers. Electron correlations are conventionally probed in noise measurements, which are technically challenging due to the difficulty to exclude the influence of external noise sources in the experimental setup. Using real-time charge detection techniques, we circumvent the problem by studying the electron correlation directly from the counting statistics of the tunneling electrons. In quantum dots, we find that the strong Coulomb interaction makes electrons try to avoid each other. This leads to electron anti-bunching, giving stronger correlations and reduced noise compared to a current carried by statistically independent electrons. The charge detector is implemented by monitoring changes in conductance in a nearby capacitively coupled quantum point contact. We find that the quantum point contact not only serves as a detector but also causes a back-action onto the measured device. Electron scattering in the quantum point contact leads to emission of microwave radiation. The radiation is found to induce an electronic transition between two quantum dots, similar to the absorption of light in real atoms and molecules. Using a charge detector to probe the electron transitions, we can relate a single-electron tunneling event to the absorption of a single photon. Moreover, since the energy levels of the double quantum dot can be tuned by external gate voltages, we use the device as a frequency-selective single-photon detector operating at microwave energies. The ability to put an on-chip microwave detector close to a quantum conductor opens up the possibility to investigate radiation emitted from mesoscopic structures and gives a deeper understanding of the role of electron–photon interactions in quantum conductors. A central concept of quantum mechanics is the wave–particle duality; matter exhibits both wave- and particle-like properties and cannot be described by either formalism alone. To investigate the wave properties of the electrons, we perform experiments on a structure containing a double quantum dot embedded in the Aharonov–Bohm ring interferometer. Aharonov–Bohm rings are traditionally used to study interference of electron waves traversing different arms of the ring, in a similar way to the double-slit setup used for investigating interference of light waves. In our case, we use the time-resolved charge detection techniques to detect electrons one-by-one as they pass through the interferometer. We find that the individual particles indeed self-interfere and give rise to a strong interference pattern as a function of external magnetic field. The high level of control in the system together with the ability to detect single electrons enables us to make direct observations of non-intuitive fundamental quantum phenomena like single-particle interference or time–energy uncertainty relations.


Physical Review Letters | 2009

Gate-controlled spin-orbit interaction in a parabolic GaAs/AlGaAs quantum well.

M. Studer; Gian Salis; Klaus Ensslin; D. C. Driscoll; A. C. Gossard

We study the tunability of the spin-orbit interaction in a two-dimensional electron gas with a front and a back gate electrode by monitoring the spin precession frequency of drifting electrons using time-resolved Kerr rotation. The Rashba spin splitting can be tuned by the gate biases, while we find a small Dresselhaus splitting that depends only weakly on the gating. We determine the absolute values and signs of the two components and show that for zero Rashba spin splitting the anisotropy of the spin-dephasing rate vanishes.


Applied Physics Letters | 2008

1.55μm ultrafast photoconductive switches based on ErAs:InGaAs

F. Ospald; D. Maryenko; K. von Klitzing; D. C. Driscoll; M. Hanson; Hong Lu; A. C. Gossard; J. H. Smet

The electron capture time in superlattice structures consisting of periodically spaced layers of self-assembled ErAs nanoislands and In0.53Ga0.47As is investigated on photoconductive switches as a function of the superlattice period using photocurrent autocorrelation and pulsed laser excitation at 1.55μm. The capture time can be tuned from picoseconds all the way down to 0.2ps by changing the periodicity. Two different Be doping schemes are explored to reduce the dark current. The resulting characteristics indicate that ErAs:InGaAs may serve as a high performance photoconductive material at this wavelength for pulsed terahertz emission and detection.

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A. C. Gossard

University of California

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Klaus Ensslin

Solid State Physics Laboratory

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Thomas Ihn

Solid State Physics Laboratory

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M. Hanson

University of California

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R. Leturcq

Centre national de la recherche scientifique

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R. Schleser

Solid State Physics Laboratory

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Simon Gustavsson

Solid State Physics Laboratory

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S. Malzer

University of Erlangen-Nuremberg

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E. R. Brown

Wright State University

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