Current Filamentation in Dipolar Electric Fields

Abstract

In the first part of this contribution we report on filamentary current flow in epitaxial n-GaAs between two ohmic point contacts. A scanning laser microscope technique has revealed two types of filamentary structure: large-area filaments, typically appearing at higher sample currents, and bendable filaments, arising at low currents and becoming curved in perpendicular magnetic fields. In the case of large-area filaments self-organization is suppressed by the dipolar field distribution from the point contacts. Numerical simulations, based on the two-level model of Schöll, have been carried out for this case.

The second part discusses the response of the sample in the filamentary current regime to local interband illumination. Repetitive current pulses have been found to occur with a mean period strongly depending on the light intensity. Statistical properties of the pulse series on a large time scale reveal features, typical of a nonlinear dynamical system. A physical mechanism is proposed, which relates the pulse occurrence to a specific switching phenomenon in the region of the filament boundary.