Solitary current-density patterns in thin ZnS:Mn films.

We experimentally investigate pattern formation phenomena in the electroluminescence of ac-driven ZnS:Mn thin films. Under suitable driving conditions, certain samples show a broad spectrum of patterns, which ranges from stationary filamentary distributions to traveling fronts and pulses. We present a survey of the bifurcation scenarios, choosing the frequency and amplitude of the driving voltage as bifurcation parameters.

Pattern formation in semiconductors.

In semiconductors, nonlinear generation and recombination processes of free carriers and nonlinear charge transport can give rise to non-equilibrium phase transitions, . At low temperatures, the basic nonlinearity is due to the autocatalytic generation of free carriers by impact ionization of shallow impurities. The electric field accelerates free electrons, causing an abrupt increase in free carrier density at a critical electric field.