Search Results (5 total)

The dominant role of grain boundary scattering in the low-temperature resistivity of both SiO₂ and Ta/SiO₂ encapsulated Cu thin films is demonstrated by the experimental variation and quantification of film thickness, roughness, and grain size. The independent variation in film thickness (28–158 nm) and grain size (35–466 nm) is achieved through subambient temperature film deposition followed by annealing. Experimentally measured film resistivities are compared with both surface scattering and grain boundary scattering models for the classical size effect, showing the dominance of the latter.

The paper introduces a set of formative assessment tasks and rubrics that were developed for use in an introductory physics instruction to help students acquire and self-assess various scientific process abilities. We will describe the rubrics, tasks, and the student outcomes in courses where the tasks and rubrics were used.

Before annealing, low-temperature-grown GaAs contains excess As which is distributed throughout the bulk in the form of point defects that clearly dominate the material’s electronic properties. Upon annealing at 600 °C, however, As precipitates are formed which can be readily observed by use of transmission electron microscopy. There has been considerable debate as to whether the electronic properties of the annealed material are controlled by these precipitates, or by residual point defects remaining in the surrounding GaAs. In this paper, we review the relevant data and issues regarding the mechanisms of point-defect-mediated compensation versus the As-precipitate, internal-Schottky-barrier model. In addition, we present data from rapid-thermal-annealing studies of the resistivity-versus-precipitate distribution, and from electromodulation measurements of Fermi-level positions in as-grown and annealed material on both n⁺- and p⁺-type substrates. These and existing data confirm that the controlling mechanism in the annealed material (GaAs:As) is indeed that of Schottky-barrier-controlled internal pinning on metallic As precipitates.

We have studied theoretically the magnetoconductance oscillations in a quasi-one-dimensional electron gas with a parabolic transverse confining potential. The solution to Schrödinger's equation is that of a hybrid harmonic oscillator with a frequency ω that depends on both the parabolic potential and the magnetic field B. At B=0, ω equals the classical oscillation frequency of the parabolic potential. In the high-field limit, ω approaches the cyclotron frequency. The result is a nonlinear fan plot for the magnetoconductance minima, which should help to clarify the origin of conductance oscillations in narrow-channel metal-oxide-semiconductor field-effect transistors.

We present results of conductance measurements of ultranarrow inversion layers in which averaging has resulted in what we believe to be a clear observation of a quasi one-dimensional density of states. A 0.2-μm-period grating gate is used to produce 250 inversion lines in parallel, each of which is Å50 nm wide and 10 μm long. Summing the conductance of these lines results in a signal-to-noise improvement of of sqrt[250] (Å16) which has enabled the observation of the quasi one-dimensional conductance oscillation.