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A contacted electroreflectance technique was used to investigate AlGaN/GaN heterostructures and their intrinsic electric field-induced properties. By studying variations in the electroreflectance with applied field, spectral features associated with the AlGaN barrier, the two-dimensional electron gas at the interface, and bulk GaN were identified. Barrier-layer composition and electric field were determined from the AlGaN Franz–Keldysh oscillations. For a high mobility heterostructure grown on SiC, measured AlGaN polarization electric field and two-dimensional electron gas density approached values predicted by a standard bandstructure model. The two-dimensional electron gas produced a broad, field-tunable first derivative electroreflectance feature. With a dielectric function calculation, we describe the line shape and relative amplitude of the two-dimensional electron gas electroreflectance feature for a wide range of electron density and applied field values.

The transformation of the small‐signal energy and momentum of a wave between two inertial reference frames as first given by Sturrock are derived by using simple perturbation theory and the appropriate transformations of length, time, current, and electromagnetic fields. The approach allows a straightforward generalization to the case of relativistic linear transformations and to nonrelativistic transformations between two reference frames that rotate with respect to each other. These rotating and linear transformations allow one to make very general statements about the frequency and wavenumbers for which negative‐energy waves are obtained in a rotating and translating medium, as, for example, an electron beam in Brillouin flow.

The nonlinear behavior of traveling‐wave amplifiers using transverse interaction modes (cyclotron and synchronous beam waves) is analyzed theoretically. An analytical solution for the circuit field amplitude as a function of distance is derived, under the assumption of a relatively slow growth per wavelength. Detailed calculations of the saturation characteristics (output power versus input power) are presented for several cases, and it is shown how the electronic efficiency can be improved by operating at a beam voltage above the synchronous voltage.

The tunnel cathode consists of a metal‐insulator‐metal sandwich in which the electrons tunnel through the insulator material. This paper presents an analysis of the noise associated with the space‐charge waves of a beam emitted from such a cathode. The beam noise temperature for a refrigerated tunnel cathode is shown to be 2730 δ, where δ is the value in volts of a built‐in energy window for the emitted electrons. The value of δ is adjustable by means of a dc potential. Assuming a beam noise temperature of 30°K, the current density is calculated for a variety of cathode parameters. A discussion is presented of the significance of the parameters and of the difficulties which would be encountered in constructing such cathodes for low noise.

The propagation of surface waves along a plasma column of annular cross section was investigated experimentally. The laboratory plasma used for the experiment was a mercury‐vapor dc discharge. The properties of the experimental discharge tube were examined to show some basic differences between the laboratory plasma and the idealized model of the plasma used for the analysis. In particular, a radially non‐uniform density distribution and the variation of the distribution with the applied magnetic field was noted. In spite of the radial‐density inhomogeneity, the experimentally determined phase constants of the backward‐surface wave are in good agreement with values predicted from the uniform density theory. The attenuation in the absence of the magnetic field is consistent with collisional losses, predominantly with the walls of the container. The effect of an axial magnetic field on the surface‐wave characteristics is examined. Experimental results show that in the presence of a magnetic field the attenuation of the backward wave is markedly increased; this enhancement of the damping is not consistent with simple collision theory within the framework of the uniform‐density model.