Chaotic motion of space charge wave fronts in semiconductors under time-independent voltage bias

A standard drift-diffusion model of space charge wave propagation in semiconductors has been studied numerically and analytically under de voltage bias. For sufficiently long samples, appropriate contact resistivity, and applied voltage-such that the sample is biased in a regime of negative differential resistance-we find chaos in the propagation of nonlinear fronts (charge monopoles of alternating sign) of electric field. The chaos is always low dimensional, but has a complex spatial structure; this behavior can be interpreted using a finite-dimensional asymptotic model in which the front (charge monopole) positions and the electrical current are the only dynamical variables.