W. Clauss

Imaging of spatio-temporal structures in semiconductors

Abstract Starting from a characterization of the spatio-temporal behavior of different semiconductor systems based upon the impact ionization of shallow impurities by hot charge carriers, we present experimental results concerning imaging of both stationary and dynamical structures by means of low-temperature scanning electron microscopy.

Critical Dynamics near the Onset of Spontaneous Oscillations in p-Germanium

The electrical avalanche breakdown of p-doped germanium at low temperatures displays self-generated current oscillations. The investigation of the transition from a stable fixed point to a limit cycle yields a scaling behaviour known from the saddle node bifurcation on a limit cycle.

Dynamics of current filaments in p-type germanium under the influence of a transverse magnetic field

An explanation for the self‐generated formation of spontaneous current oscillations developing during low‐temperature impact ionization breakdown of slightly doped p‐type germanium is presented for the first time, taking advantage of a model experiment. Upon applying a relatively small transverse magnetic field, the spatially inhomogeneous current distribution manifest in the form of individual high‐conducting‐current filaments undergoes a distinct traveling dynamics that is oriented perpendicular to the direction of the electric and the magnetic field (i.e., not coincident with the direction of the current flow). The resulting magnetic‐field‐induced oscillatory behavior can be described qualitatively by simple model considerations.

Evidence of Type-III Intermittency in the Electric Breakdown of p-Type Germanium

Electric oscillations arising spontaneously in the low-temperature avalanche breakdown of p-germanium are investigated with respect to the intermittent routes to chaos. The experimental data display several universal features of type-III intermittency.

Electron-beam induced instability during filamentary current transport inn-GaAs

We report experimental investigations on the current transport ofn-GaAs under the conditions of impact ionization avalanche breakdown at low temperatures. The spontaneous formation of a single current filament was observed by means of low-temperature scanning electron microscopy. An electron-beam induced instability occurs at the onset of filamentation. We demonstrate this instability to be due to the local disturbance at the boundaries of the current filament. Our results are compared to the similar behavior ofn-GaAs under IR irradiation (firing wave instability).

Self-Organized Critical Behaviour in the Low-Temperature Impact Ionization Breakdown of p-Ge

We have investigated slightly doped p-Ge at the onset of impact ionization breakdown. The statistical temporal distribution of the breakdown events exhibits a power law behaviour supporting the model of self-organized criticality introduced by Bak, Tang and Wiesenfeld.

Circuit-limited oscillation at the onset of avalanche breakdown in semiconductors

Abstract Experimental evidence of one simple type of oscillation, arising in the instability region of electric breakdown, is given. Presenting different semiconductor systems (p-Ge and two types of n-GaAs), we show conditions under which this instability is favored to other competing instabilities.

Impact ionization avalanche breakdown in short crystal regions of p‐Ge

The low‐temperature impact ionization avalanche breakdown in p‐Ge is investigated on a series of samples with various lengths of the electrically active region located between the ohmic contacts. We have studied the breakdown behavior as a function of the contact distance together with the response to an applied magnetic field. A simple model considering the specific hot‐carrier situation in the prebreakdown regime can explain the experimental results.

Resonant imaging of a critical dynamical state in the low-temperature electric transport of p-Ge

Abstract We report on the critical dynamical behavior of p-Ge near the onset of impact ionization avalanche breakdown at liquid-helium temperatures. In addition to the analysis of temporal signals, we have investigated the spatial character of the instability by means of low-temperature scanning electron microscopy and electron-beam-induced resonance. From our results, we conclude that spatial degrees of freedom are fully involved in the critical dynamical process. The spatio-temporal behavior of our experimental system is compared to the model of self-organized criticality.

Spatio — Temporal Correlations in Semiconductors

The electric avalanche breakdown of homogeneously doped semiconductors at low temperatures can be regarded as a nonequilibrium phase transition. If this breakdown is associated with negative differential conductivity, i.e. bistabihty between a low and a high conducting phase, spontaneous structure formation occurs. Current filaments as spatial structures and spontaneous oscillations as temporal structures were observed. Both structures are in close connection to each other. At the very onset of the breakdown, no stable filament can be created. Here, a firing mode of filaments was observed which displays critical dynamics like 1/f noise. The analogy to the self-organized criticality is discussed. In the breakdown regime with sufficient power dissipation, stable filaments were observed. These filaments may display low-dimensional nonlinear dynamics due to small structural changes like a breathing mode. Evidence is presented that typical nonlinear dynamics like quasiperiodicity and chaos is due to the nonlinear interaction of spatially localized oscillation centers.