Escape Frequency Research Articles

A.C. behavior of damaged surface layers on CdS crystals

Damaged surface layers on the (0001) and (000 1 ) faces of CdS crystals display the high resistance and capacitance characteristic of large trap concentrations when measured over the frequency range from 10 2 to 10 6 c/s. Changes observed in the characteristic relaxation spectra as d.c. bias is increased are interpreted in terms of an exponential dependence of the escape frequency of trapped carriers on the electric field. Ambient effect data and their interpretation are also included.

Attenuation and group retardation in the ionosphere

Expressions are derived from the Appleton-Hartree formula for the specific attenuation and group velocity at any given height, in a layer with a vertical electronic gradient, for a wave of any given frequency at vertical incidence in the presence of an oblique magnetic field. They are then used to study the overall attenuation and group retardation of a wave which either is reflected from the layer, or penetrates through it to be returned from a denser layer above. To do this in detail, a definite type of layer has to be assumed, and particular values have to be chosen for the frequency of the wave and the direction and magnitude of the earth's magnetic field, so that the results can be compared with typical experimental data obtained by the usual P' f and P' t technique. The analysis shows that, as one would expect from general physical principles, the attenuation and group delay for a wave near to the critical escape frequency occur mainly in the region of maximum density in the layer, and also justifies the use of absorption and equivalent-height measurements to deduce an estimate of the collisional frequency of the electrons in this region. The problem is worked out in detail for one frequency for the extraordinary wave, for values of the earth's field and the angle of the dip corresponding roughly to the values for London, and for a parabolic and a sine-squared law of electronic density. The work falls into four main sections: (a) the derivation of the integrals from the Appleton-Hartree formula; (b) the effect of the type of the layer on the form of the integrals; (c) the application of a graphical method of integration, involving the initial transformation of the integrals to a form in which they can be accurately evaluated; (d) the detailed working out of a numerical example, with a discussion of the general conclusions to be drawn from it. It is hoped that the fundamental results for the specific attenuation and group velocity, on which the rest of the paper is based, may prove useful in other investigations.