Far-infrared radiation controlled chaos in n-GaAs

Abstract

The effect of far-infrared irradiation on selfgenerated periodic and chaotic current fluctuations in the post-breakdown regimes of n-GaAs has been investigated at liquid helium temperature. In an external magnetic field of 40 nat the material showed a sequence of frequency-locked oscillations being ordered according to the Farey-Tree. Depending on the irradiation intensity a shifting and scaling of the bias voltage ranges of the frequency-locking states has been observed.Chaos theory has become one of the most powerful tools in describing the dynamics of nonlinear systems. Besides classical disciplines, nonlinear and chaotic transport phenomena in semiconductors show the wide spectrum of different types of chaotic behavior. These nonlinear spatic~temporal effects have been observed by current fluctuations in Ge [1][2][3][4][5][6], Si [71, InSb [8] and GaAs [9][10][11][12]. Especially the alternating sequence of periodic and chaotic behavior can be treated in terms of the circle-map theory. Although the phenomenological theory sets guidelines for modelling the underlying microscopic mechanisms, the elementary processes causing the observed instabilities are still not well understood.Previous results obtained from selfgenerated current fluctuations in n-OaAs epitaxial layers, demonstrate the crucial role of an external magnetic field and of the free carrier concentration. For vanishing magnetic field strength only regular relaxation oscillations occur with frequencies up to about 5 MHz, depending on the sample and the bias voltage. Applying a magnetic field as weak as 10 mT and varying the bias voltage a sequence of regular oscillations, quasiperiodic behavior showing two independent frequencies, frequency-locking and a Ruelle-Takens-Newhouse scenario have been observed, occuring in well defined voltage ranges [11,12].In the present study we observed that also far-infrared irradiation of the samples affects the nonlinear dynamics of the electrons in a very sensitive way. Low power FIR irradiation constitutes a linear free carrier generation mechanism, whose rate is easily controllable by varying the intensity, influencing the nonlinear generationrecombination kinetics and transport properties. Our measurements show that the overa!i qualitative behavior of the time series of the current through the sample and the spectral characteristics of the fluctuations remain unaltered for different control parameter regimes. However, even very low irradiation intensity rescales the voltage ranges of the above mentioned fluctuations and shifts the voltage ranges to higher values. The experimental results will be discussed in terms of the circlemap theory.The measurements have been carried out on n-GaAs epitaxial layers. Samples were mounted in the center of a superconducting solenoid and immersed in liquid helium at 4.2K. The magnetic field was perpendicular to the current through a sample and to the sample surface, parallel to the [100] crystallographic direction. FIR radiation of 337 #m wavelength from a cw HCNlaser was gu...

Dark current characterization of photoconductive switches

“…Efforts were thwarted by unexpected spontaneous current oscillations which were subsequently studied in some detail [9]. More recently, semiconductor current fluctuations have received attention in the field of nonlinear and chaotic dynamics [10][11][12][13], and have proven to be a stubborn noise source in GaAs integrated circuits and discrete devices. Consequences have included modulation of the width of the channeVsubsirate space charge region in MESFETs, thus giving an amplified version of the LFO at the output [14].…”