Sequence of different types of nonlinear current oscillation in n-GaAs

Abstract

Abstract. Self-generated chaotic current fluctuations in the post-breakdown regime of a n-GaAs layer at 4.2 K have been analyzed in detail. Without an external magnetic field only regular oscillations were observed. Increasing the magnetic field strength up to 100mT generates a sequence of quasiperiodic and frequency-locking current oscillations and finally a Ruelle-Takens-Newhouse scenario with chaos. This may be understood by assuming two coupled oscillatory processes caused by dielectric relaxation and energy relaxation in the distribution of free carriers. 05.40., 72.70., 72.20J High-purity semiconductors at low temperature show highly nonlinear current-voltage characteristics. For small electric fields almost all carriers are bound to shallow impurities yielding a low conductance of the sample. At a critical field of a few volts per cm the impact ionization rate of shallow impurities exceeds the capture rate for low carrier concentration resulting in a rapid increase of the current. The steady-state properties of the transition from the low-conducting state to the high-conducting state have been analyzed in terms of nonequilibrium phase transformations 1-14]. In the course of the transition, spontaneous oscillations and chaotic current fluctuations have been observed in several semiconductor materials 1,5-17]. Different types of, and routes to, chaos were recognized and discussed in terms of nonlinear dynamics [18][19][20][21][22][23][24][25][26][27][28]. Current fluctuations in semiconductors may occur spontaneously I-5-13] or be induced by an external periodic driving force 1-13-17]. PACS:In the present paper we report on a detailed study of self-generated current fluctuations in high purity n-GaAs epitaxial layers which occur within a limited bias voltage interval in the post-breakdown regime of the material. The observed phenomena depend critically on the strength of an external magnetic field. At zero field, B = 0, only regular oscillations were found. Increasing B up to not more than 100mT causes a sequence of quasiperiodic and frequency-locking current phenomena, finally undergoing a Ruelle-TakensNewhouse scenario to chaos. This behavior may be attributed to the coupling of two oscillatory processes, in the present case dielectric relaxation and an oscillation of the nonequilibrium electron distribution. The experimental results are in excellent agreement with the predictions of the circle-map theory. The coupling strength, frequencies and amplitudes of both selfsustained processes depend strongly on the magnetic field strength.

Far-infrared radiation controlled chaos in n-GaAs

“…In agreement to previous investigations on various samples [12], in the absence of a magnetic field the system is forming coherent oscillations for currents well above the breakdown. Subjecting the sample to a small magnetic field may cause quasiperiodic and frequency- The overlap of two or more locking states on the voltage scale causes a 'frustrated' chaotic behavior [13] of the current fluctuations.…”

“…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.…”

“…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].…”

“…Above that critical voltage oscillations and fluctuations of the current arise in distinct voltage intervals. In order to localize the regions in the current-voltage plane where fluctuations occur, the current-voltage characteristics for different FIR powers were recorded by a dynamical method [12], displayed in Fig.1. The hatched areas in the current-voltage plane indicate the extension of fluctuations.…”

“…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.…”