J. A. Seamons

Sandia National Laboratories, Albuquerque, New Mexico, United States

Are you J. A. Seamons?

Claim your profile

Publications (19)31.66 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A low-temperature upturn of the Coulomb drag resistivity rhoD measured in undoped electron-hole bilayer devices, possibly manifesting from formation of a superfluid condensate or density modulated state, was recently observed. Here the effects of perpendicular and parallel magnetic fields on the drag upturn are examined. Measurements of rhoD and drive layer resistivity rhoxx-e as a function of temperature and magnetic field in two uEHBL devices are presented. In B, the drag upturn was enhanced as the field increased up to roughly .2 T, beyond which oscillations in rhoD and rhoxx-e, reflecting Landau level formation, begin appearing. A small phase offset between those oscillations, which decreased at higher fields and temperatures, was also observed. In B||, the drag upturn magnitude diminished as the field increased. Above the upturn regime, both rhoD and rhoxx-e were enhanced by B||, the latter via decreased screening of the uniform background impurities. This work has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.
    03/2010;
  • Source
    E Bielejec, J A Seamons, M S Carroll
    [Show abstract] [Hide abstract]
    ABSTRACT: Electronic devices that are designed to use the properties of single atoms such as donors or defects have become a reality with recent demonstrations of donor spectroscopy, single photon emission sources, and magnetic imaging using defect centers in diamond. Ion implantation, an industry standard for atom placement in materials, requires augmentation for single ion capability including a method for detecting a single ion arrival. Integrating single ion detection techniques with the single donor device construction region allows single ion arrival to be assured. Improving detector sensitivity is linked to improving control over the straggle of the ion as well as providing more flexibility in lay-out integration with the active region of the single donor device construction zone by allowing ion sensing at potentially greater distances. Using a remotely located passively gated single ion Geiger mode avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency at a distance of >75 microm from the center of the collecting junction. This detection efficiency is achieved with sensitivity to approximately 600 or fewer electron-hole pairs produced by the implanted ion. Ion detectors with this sensitivity and integrated with a thin dielectric, for example a 5 nm gate oxide, using low energy Sb implantation would have an end of range straggle of <2.5 nm. Significant reduction in false count probability is, furthermore, achieved by modifying the ion beam set-up to allow for cryogenic operation of the SIGMA detector. Using a detection window of 230 ns at 1 Hz, the probability of a false count was measured as approximately 10(-1) and 10(-4) for operation temperatures of approximately 300 K and approximately 77 K, respectively. Low temperature operation and reduced false, 'dark', counts are critical to achieving high confidence in single ion arrival. For the device performance in this work, the confidence is calculated as a probability of >98% for counting one and only one ion for a false count probability of 10(-4) at an average ion number per gated window of 0.015.
    Nanotechnology 02/2010; 21(8):85201. · 3.84 Impact Factor
  • J. A. Seamons, E. Bielejec, M. S. Carroll
    [Show abstract] [Hide abstract]
    ABSTRACT: Donor based qubits in Si for solid-state quantum information processing require precise dopant placement into the bulk Si. Placement precision donor is limited by straggle which is strongly dependant upon dopant selection and implantation energy, therefore detection of low energy ions (
    03/2009;
  • Source
    J A Seamons, C P Morath, J L Reno, M P Lilly
    [Show abstract] [Hide abstract]
    ABSTRACT: Electron-hole bilayers are expected to make a transition from a pair of weakly coupled two-dimensional systems to a strongly coupled exciton system as the barrier between the layers is reduced. Coulomb drag measurements on devices with a 30 nm barrier are consistent with two weakly coupled 2D Fermi systems where the drag decreases with temperature. For a 20 nm barrier, however, we observe an increase in the drag resistance as the temperature is reduced when a current is driven in the electron layer and voltage measured in the hole layer. These results indicate the onset of strong coupling possibly due to exciton formation or phenomena related to exciton condensation.
    Physical Review Letters 02/2009; 102(2):026804. · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on the fabrication and performance of a novel single ion Geiger mode avalanche (SIGMA) diode detector that senses single ions with ∼ 100% detection efficiency at room temperature for 250 keV protons. The SIGMA diode detector utilizes Geiger mode operation of avalanche photodiodes, which can be sensitive to single electron-hole (e-h) pairs induced by the ion stopping. The SIGMA diode detector takes advantage of a complementary metal oxide semiconductor foundry allowing for future integration with silicon nanostructures to build novel single atom modified devices. SIGMA diode detector offers potential improvement in current integrated ion detector approaches that have noise floors in the order of 103 e-h pairs.
    Applied Physics Letters 07/2008; 93(4):043124-043124-3. · 3.79 Impact Factor
  • Source
    J. A. Seamons, M. S. Carroll
    [Show abstract] [Hide abstract]
    ABSTRACT: There is increasing interest in development of high speed, low noise and readily fieldable near infrared (NIR) single photon detectors. InGaAs/InP Avalanche photodiodes (APD) operated in Geiger mode (GM) are a leading choice for NIR due to their preeminence in optical networking. After-pulsing is, however, a primary challenge to operating InGaAs/InP single photon detectors at high frequencies1. After-pulsing is the effect of charge being released from traps that trigger false ("dark") counts. To overcome this problem, hold-off times between detection windows are used to allow the traps to discharge to suppress after-pulsing. The hold-off time represents, however, an upper limit on detection frequency that shows degradation beginning at frequencies of ~100 kHz in InGaAs/InP. Alternatively, germanium (Ge) single photon avalanche photodiodes (SPAD) have been reported to have more than an order of magnitude smaller charge trap densities than InGaAs/InP SPADs2, which allowed them to be successfully operated with passive quenching2 (i.e., no gated hold off times necessary), which is not possible with InGaAs/InP SPADs, indicating a much weaker dark count dependence on hold-off time consistent with fewer charge traps. Despite these encouraging results suggesting a possible higher operating frequency limit for Ge SPADs, little has been reported on Ge SPAD performance at high frequencies presumably because previous work with Ge SPADs has been discouraged by a strong demand to work at 1550 nm. NIR SPADs require cooling, which in the case of Ge SPADs dramatically reduces the quantum efficiency of the Ge at 1550 nm. Recently, however, advantages to working at 1310 nm have been suggested which combined with a need to increase quantum bit rates for quantum key distribution (QKD) motivates examination of Ge detectors performance at very high detection rates where InGaAs/InP does not perform as well. Presented in this paper are measurements of a commercially available Ge APD operated at relatively short GM hold-off times to examine whether there are potential advantages to using Ge for 1310 nm single photon detection. A weaker after-pulsing dependence on frequency is observed offering initial indications of the potential that Ge APDs might provide better high frequency performance.
    Proc SPIE 05/2008;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recently interest in the layer interdependence of a bilayer's transport has emerged. To examine this dependence the layer transport properties in an undoped electron-hole bilayer (uEHBL) device were measured as a function of density, inter-layer electric field and temperature. The uEHBL device consisted of a tunable, independently-contacted two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) induced in distinct GaAs quantum wells separated by a 30 nm Al.9Ga.1 As barrier. At T = 0.3 K, the 2DHG mobility increased with increasing 2DEG density, while the opposite effect was not observed. Decreasing the inter-layer electric field also increased 2DHG mobility without affecting the 2DEG mobility. This also decreased 2DHG Coulomb drag suggesting the inter-layer separation was increased. Distinct temperature dependencies were also measured for each layer's density and resistivity.
    Physical review. B, Condensed matter 03/2008; · 3.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Since it was predicted over two decades ago, there has been intense interest in exciton condensation in coupled-well bilayer systems. While exciton condensation effects have been evident in optically-generated indirect excitons and quantum Hall bilayers, transport experiments in electron-hole bilayers in the regime of exciton condensation have proven to be extremely difficult. Results of Coulomb drag (rhoDRAG) measurements at zero magnetic field on new undoped electron-hole bilayer devices formed in GaAs/Al0.9Ga0.1As double quantum well heterostructures are presented. For devices with 30 nm barriers rhoDRAG demonstrates T^2 behavior consistent with two Fermi liquids. In 20 nm barrier devices a dramatic upturn in the 2DHG Coulomb drag voltage occurs below T=1K. This upturn signals an increase in inter-layer coupling consistent with exciton formation. This work has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.
    03/2008;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the fabrication details of completely undoped electron-hole bilayer devices in a GaAs/AlGaAs double quantum well heterostructure with a 30 nm barrier. These devices have independently tunable densities of the two-dimensional electron gas and two-dimensional hole gas. We report four-terminal transport measurements of the independently contacted electron and hole layers with balanced densities from $1.2 \times 10^{11}$cm$^{-2}$ down to $4 \times 10^{10}$ cm$^{-2}$ at $T = 300 mK$. The mobilities can exceed $1 \times 10^{6}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for electrons and $4 \times 10^{5}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for holes. Comment: 3 pages, 3 figures
    Applied Physics Letters 11/2006; · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We study two-dimensional to two-dimensional (2D–2D) tunneling between two electron layers separated by a wide barrier in an in-plane magnetic field B. The electron gases are separately in equilibrium with their chemical potentials displaced by the bias energy V. We show for a general electronic structure that the tunneling current shows a “fish-like” domain shape on the Δk-V plane where Δk∝B is the B-induced wave number displacement. The domain shape is determined by the Fermi energies and wave numbers. The boundaries between the high-, low-, and zero-current regions are sharp, representing the high differential conductance and are made of a combination of regular, inverted, and shifted energy-dispersion curves. This result is also valid for 2D–1D and 1D–1D tunneling. The observed data for the 2D–2D tunneling currents as well as the differential conductance in GaAs/AlxGa1-xAs double quantum wells yield good agreement with the predicted domain shape.
    Physica E Low-dimensional Systems and Nanostructures 01/2006; 34:425-428. · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report low-dimensional tunneling in an independently contacted vertically coupled quantum wire system. This nanostructure is fabricated in a high-quality GaAs/AlGaAs parallel double quantum well heterostructure. Using a novel flip chip technique to align top and bottom split gates to form low-dimensional constrictions in each of the independently contacted quantum wells we explicitly control the subband occupation of the individual wires. Our designed geometry includes simultaneous measurement of both the 2D–2D and 1D–1D tunneling regimes. In addition to the expected 2D–2D tunneling results, we have found additional tunneling features that are related to the 1D quantum wires.
    Physica E Low-dimensional Systems and Nanostructures 01/2006; 34(1):433-436. · 1.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report tunneling measurements between two vertically coupled quantum wires in a GaAs/AlGaAs double quantum well structure with a 7.5 nm barrier. Split gates above and below the electron bilayer define each quantum wire and allow separately controlled 1D densities. Separate contacts are achieved with additional depletion gates. Parallel conductance as a function of split gate voltages provides a map of the 1D subband occupation; tunneling measurements can be made with any combination of subbands occupied in each wire. The full tunneling spectroscopy is measured using both a voltage between the wires and parallel magnetic field to explore the energy and momentum dependence of the tunneling. We observe a number of features, such as resonance peaks at high parallel magnetic fields, that can be explained within the framework of non- interacting 1D systems. These resonance features change in a systematic way as the number of occupied subbands changes. Other characteristics of the data such as very broad tunnel resonances as a function of the interwire voltage may require many-body interactions for a complete description of the tunneling physics. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04- 94AL85000.
    01/2006;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report low-dimensional transport and tunneling in a vertically coupled quantum wire system. The quantum wires are fabricated in a high quality parallel double quantum well electron systems, with well widths of 18 nm and a barrier thickness between the wells ranging from 7.5 to 20 nm. Using a technique developed at Sandia we use symmetric top and bottom split-gates to form low-dimensional constrictions in each of the independently contacted quantum wells. This configuration allows for the study of 2D-2D, 2D-1D and 1D-1D behaviors. We will discuss tunneling conductance as the temperature, magnetic-field, and dimensionality are varied. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
    06/2005;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The temperature dependence of the resistivity and magnetoresistance of dilute 2D electrons are reported. The temperature dependence of the resistivity can be qualitatively described through phonon and ionized impurity scattering. While the temperature dependence indicates no ln(T) increase in the resistance, a sharp negative magnetoresistance feature is observed at small magnetic fields. This is shown to arise from weak localization. At very low density, we believe weak localization is still present, but cannot separate it from other effects that cause magnetoresistance in the semi-classical regime.
    01/2005;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report a study on the uniformity of long quantum wires in the crossover from ballistic to diffuse transport with lengths ranging from 1 μm to 20 μm. For the 1 μm wire we measure 15 plateaus quantized at integer values of 2e2/h. With increasing length we observe plateaus at conductance values suppressed below the quantized values. With nonlinear fitting to the magnetoresistances we obtain an effective width for the quantum wires. As we find no systematic variation of the effective width as a function of sublevel index for the various length wires, we conclude that we have uniform long single quantum wires up to 20 μm.
    01/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report low-dimensional tunneling in an independently contacted vertically coupled quantum wire system. This nanostructure is fabricated in a high quality GaAs/AlGaAs parallel double quantum well heterostructure. Using a novel flip chip technique to align top and bottom split gates to form low-dimensional constrictions in each of the independently contacted quantum wells we explicitly control the subband occupation of the individual wires. In addition to the expected 2D-2D tunneling results, we have found additional tunneling features that are related to the 1D quantum wires. Comment: 4 pages, 3 figures, submitted to APL Minor revisions
    Applied Physics Letters 11/2004; · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: While quantized conductance steps in short quantum wires are understood through a single electron picture, additional structure often observed in high-quality one-dimensional systems near g=0.7×(2e2/h) is commonly interpreted as arising due to many-body interactions. Most studies of conductance structure below 2e2/h use short one-dimensional wires where transport is known to be ballistic. We report transport measurements for both short (0.5 μm) and long (5 μm) quantum wires, and use both conductance and nonlinear transport to explore the behavior of one-dimensional wires.
    Superlattices and Microstructures 01/2003; 34:493-496. · 1.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: For several years now quantum computing has been viewed as a new paradigm for certain computing applications. Of particular importance to this burgeoning field is the development of an algorithm for factoring large numbers which obviously has deep implications for cryptography and national security. Implementation of these theoretical ideas faces extraordinary challenges in preparing and manipulating quantum states. The quantum transport group at Sandia has demonstrated world-leading, unique double quantum wires devices where we have unprecedented control over the coupling strength, number of 1 D channels, overlap and interaction strength in this nanoelectronic system. In this project, we study 1D-1D tunneling with the ultimate aim of preparing and detecting quantum states of the coupled wires. In a region of strong tunneling, electrons can coherently oscillate from one wire to the other. By controlling the velocity of the electrons, length of the coupling region and tunneling strength we will attempt to observe tunneling oscillations. This first step is critical for further development double quantum wires into the basic building block for a quantum computer, and indeed for other coupled nanoelectronic devices that will rely on coherent transport. If successful, this project will have important implications for nanoelectronics, quantum computing and information technology.