Physics and Modeling of Submicron Devices. Annual Report: August I, 1987 - July 31, 1988

The work described in this report is directed at understanding quantum transport phenomena in sub-micron heterostructure devices, at developing computational techniques for modeling such devices, and at applying these techniques to develop new device concepts. During the past year we have (l) applied a previously developed collisionless quantum device model (SEQUAL) and Monte Carlo model (DEMON) to the design and study of heterojunction bipolar transistors (Chapter 2); (2) developed a technique for the analysis of arbitrarily shaped quantum devices with elastic scattering (Chapter 3); and (3) developed an approach for incorporating inelastic dissipative processes in quantum transport theory (Chapter 4). As a by-product of the research, several heterostructure device models have been developed: 1- and 2-D equilibrium models, 1- and 2-D drift-diffusion models, a I-D Monte Carlo simulator and a 1-D collisionless quantum device model. These simulation programs are being applied to advanced device analysis at a number of laboratories and are available to SRC members on reques

Physics and Modeling of Submicron Devices

The work described in this report is directed at understanding transport physics in sub-micron heterostructure devices, at developing computational techniques for modeling such devices, and at applying these techniques to investigate new device concepts. The focus of the past year’s work has been on extending our collisionless, quantum device models to treat elastic scattering processes and at applying previously-developed models to the design and study of AlGaAs/GaAs heterojunction bipolar transistors. This report describes the past year’s progress in these two areas. As a by-product of the research, several heterostructure device models have been developed, 1- and 2-D equilibrium models, 1- and 2-D drift-diffusion models, a 1-D Monte Carlo simulator and a 1-D, collisionless quantum device model. These simulation programs are being applied to advanced device analysis at a number of laboratories and are available to SRC members on request

Scattering properties of a cut-circle billiard waveguide with two conical leads

We examine a two-dimensional electron waveguide with a cut-circle cavity and conical leads. By considering Wigner delay times and the Landauer-B\"{u}ttiker conductance for this system, we probe the effects of the closed billiard energy spectrum on scattering properties in the limit of weakly coupled leads. We investigate how lead placement and cavity shape affect these conductance and time delay spectra of the waveguide.Comment: 18 pages, 11 figures, accepted for publication in Phys. Rev. E (Jan. 2001

Aharonov-Bohm effect and resonances in the circular quantum billiard with two leads

We calculate the conductance through a circular quantum billiard with two leads and a point magnetic flux at the center. The boundary element method is used to solve the Schrodinger equation of the scattering problem, and the Landauer formula is used to calculate the conductance from the transmission coefficients. We use two different shapes of leads, straight and conic, and find that the conductance is affected by lead geometry, the relative positions of the leads and the magnetic flux. The Aharonov-Bohm effect can be seen from shifts and splittings of fluctuations. When the flux is equal to (h/2e) and the angle between leads is 180 degree, the conductance tends to be suppressed to zero in the low energy range due to the Aharonov-Bohm effect.Comment: LaTeX2e, 8 pages, 6 figures, submitted to Phys. Rev. B (Two references added. A discussion on discrete symmetries removed.

Electronic properties of a quantum wire with arbitrary bending angle

The electron transmission and bound state properties of a quantum wire with a sharp bend at arbitrary angle are studied, extending results on the right angle sharp bend (the L¿shaped wire). These new results are compared to those of a similar structure, the circular bend wire. The possibility of using a bent wire to perform transistor action is also discussed

An improved measurement of muon antineutrino disappearance in MINOS

We report an improved measurement of muon anti-neutrino disappearance over a distance of 735km using the MINOS detectors and the Fermilab Main Injector neutrino beam in a muon anti-neutrino enhanced configuration. From a total exposure of 2.95e20 protons on target, of which 42% have not been previously analyzed, we make the most precise measurement of the anti-neutrino "atmospheric" delta-m squared = 2.62 +0.31/-0.28 (stat.) +/- 0.09 (syst.) and constrain the anti-neutrino atmospheric mixing angle >0.75 (90%CL). These values are in agreement with those measured for muon neutrinos, removing the tension reported previously.Comment: 5 pages, 4 figures. In submission to Phys.Rev.Let

Improved Search for Muon-Neutrino to Electron-Neutrino Oscillations in MINOS

We report the results of a search for ν_e appearance in a ν_μ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2×10^(20) protons on the NuMI target at Fermilab, we find 2sin^2(θ_(23))sin^2(2θ_(13))<0.12(0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin^2(θ_(23))sin^2(2θ_(13))=0.041^(+0.047)_(-0.031)(0.079^(+0.071)_(-0.053). The θ_(13)= 0 hypothesis is disfavored by the MINOS data at the 89% confidence level

New constraints on muon-neutrino to electron-neutrino transitions in MINOS

This paper reports results from a search for ν_μ → ν_e transitions by the MINOS experiment based on a 7×10^(20) protons-on-target exposure. Our observation of 54 candidate ν_e events in the far detector with a background of 49.1±7.0(stat)±2.7(syst) events predicted by the measurements in the near detector requires 2sin^2(2θ_(13))sin^2θ_(23)<0.12(0.20) at the 90% C.L. for the normal (inverted) mass hierarchy at δ_(CP)=0. The experiment sets the tightest limits to date on the value of θ_(13) for nearly all values of δ_(CP) for the normal neutrino mass hierarchy and maximal sin^2(2θ_(23))

A Study of Muon Neutrino Disappearance Using the Fermilab Main Injector Neutrino Beam

We report the results of a search for muon-neutrino disappearance by the Main Injector Neutrino Oscillation Search. The experiment uses two detectors separated by 734 km to observe a beam of neutrinos created by the Neutrinos at the Main Injector facility at Fermi National Accelerator Laboratory. The data were collected in the first 282 days of beam operations and correspond to an exposure of 1.27e20 protons on target. Based on measurements in the Near Detector, in the absence of neutrino oscillations we expected 336 +/- 14 muon-neutrino charged-current interactions at the Far Detector but observed 215. This deficit of events corresponds to a significance of 5.2 standard deviations. The deficit is energy dependent and is consistent with two-flavor neutrino oscillations according to delta m-squared = 2.74e-3 +0.44/-0.26e-3 eV^2 and sin^2(2 theta) > 0.87 at 68% confidence level.Comment: In submission to Phys. Rev.