40 research outputs found
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. In static electric fields, this nonlinearity is known to yield complex filamentary current patterns bound to electric contacts
Theory of traveling filaments in bistable semiconductor structures
We present a generic nonlinear model for current filamentation in
semiconductor structures with S-shaped current-voltage characteristics. The
model accounts for Joule self-heating of a current density filament. It is
shown that the self-heating leads to a bifurcation from static to traveling
filament. Filaments start to travel when increase of the lattice temperature
has negative impact on the cathode-anode transport. Since the impact ionization
rate decreases with temperature, this occurs for a wide class of semiconductor
systems whose bistability is due to the avalanche impact ionization. We develop
an analytical theory of traveling filaments which reveals the mechanism of
filament motion, find the condition for bifurcation to traveling filament, and
determine the filament velocity.Comment: 13 pages, 5 figure
StoĂźionisationsinduzierte Strukturbildung in Halbleitern mittels Mikrowellen
In gering dotierten Halbleiterschichten kann bei elektrischen Feldern von wenigen V/cm ein Nichtgleichgewichtsphasenübergang von einem niedrigleitenden in einen hochleitenden Zustand beobachtet werden. Bei Beschaltung mit elektrischen Gleichfeldern ist dieser Übergang mit der Ausbildung von Stromfilamenten verbunden. Erstmals wurde auch ohne elektrische Kontakte, im elektrischen Wechselfeld von Mikrowellen, die Ausbildung kreisförmiger räumlichen Strukturen in der Elektronendichte gefunden. In Abhängigkeit von der Mikrowellenleistung tritt eine deutliche Hysterese im Entstehungs- und Verlöschprozeß der mikrowelleninduzierten Strukturen auf. Die Abstände der Strukturen werden mit den Ergebnissen zweidimensionaler Berechnungen der Mikrowellenfeldverteilung verglichen
Microwave induced patterns in n-GaAs and their photoluminescence imaging
Using the technique of photoluminescence imaging, self-organized patterns of high-electron density in
homogeneous n-GaAs layers under homogeneous microwave irradiation are studied. The structures are shown
to be analogous to current filaments in a static electric field. The symmetry of the microwave induced patterns
is not constrained by the current feeding electrodes. It is, however, concluded that a feedback mechanism exists
between the formation of high-conducting structures and the homogeneity of the incident microwave
irradiation