Small-signal theory of unipolar injection currents in solids

Small-signal behavior of unipolar currents injected in semiconductors or insulators is theoretically studied. The one-dimensional problem of plane-parallel electrodes is considered. Analysis neglects diffusion but takes into account carrier mobility field dependence, ionized impurities, and trapping. Arbitrary boundary conditions are assumed. The present theory describes the small-signal response by a set of four complex quantities recalling the Llewellyn-Peterson coefficients for vacuum tubes. The present paper represents a generalization of previous results obtained by Yoshimura in the following respects: new physical phenomena (hot carrier effects and trapping) are taken into account, and new applications of the derived coefficients are suggested. This paper also contains a brief comment on physical situations and devices that can be studied by the present theory, paying particular attention to high-frequency negative-resistance devices.