Noise-enhanced chaos in a weakly coupled GaAs/(Al,Ga)As superlattice

Abstract

Noise-enhanced chaos in a doped, weakly coupled GaAs/Al_{0.45}Ga_{0.55}As superlattice has been observed at room temperature in experiments as well as in the results of the simulation of nonlinear transport based on a discrete tunneling model. When external noise is added, both the measured and simulated current-versus-time traces contain irregularly spaced spikes for particular applied voltages, which separate a regime of periodic current oscillations from a region of no current oscillations at all. In the voltage region without current oscillations, the electric-field profile consist of a low-field domain near the emitter contact separated by a domain wall consisting of a charge accumulation layer from a high-field regime closer to the collector contact. With increasing noise amplitude, spontaneous chaotic current oscillations appear over a wider bias voltage range. For these bias voltages, the domain boundary between the two electric-field domains becomes unstable and very small current or voltage fluctuations can trigger the domain boundary to move toward the collector and induce chaotic current spikes. The experimentally observed features are qualitatively very well reproduced by the simulations. Increased noise can consequently enhance chaotic current oscillations in semiconductor superlattices.

Coherence Resonance and Stochastic Resonance in an Excitable Semiconductor Superlattice

“…Recently, under dc voltage bias, spontaneously chaotic [17,18], periodic, and quasiperiodic [19] self-sustained current oscillations have been observed in GaAs=Al 0.45 Ga 0.55 As 50-period SLs at room temperature. Noise may induce or enhance chaotic oscillations over a wider voltage bias range provided its amplitude is sufficiently large and its bandwidth is much smaller than the oscillation frequency [20]. Numerical simulations show that thermal and shot noise enhance deterministic spontaneous chaos in a STET model of a SSL of 50 identical spatial periods [21,22].…”

“…The voltage noise ηðtÞ has two components: (i) η th ðtÞ, which is related to the noise of the source, and (ii) the external noise η c ðtÞ. η th ðtÞ is simulated by picking random numbers every 5 × 10 −11 s from a zero mean distribution with a standard deviation of 2 mV [20]. η c ðtÞ is a white noise with bandwidth of 1 GHz and tunable amplitude V rms noise .…”

“…These noise values have been selected so that the results of the numerical simulations of the model agree qualitatively with the results of the experiments reported in Refs. [20,25]. We have ignored the smaller value of η th ðtÞ at the SSL wells [21,22].…”

Fast Detection of a Weak Signal by a Stochastic Resonance Induced by a Coherence Resonance in an Excitable GaAs/Al0.45Ga0.55As Superlattice

“…Very recently, we investigated the effect of noise on spontaneous chaotic current oscillations in a dc-biased GaAs=Al 0.45 Ga 0.55 As SL using noise with a bandwidth much smaller than the oscillation frequency [21]. With increasing noise amplitude, the spontaneous chaotic current oscillations appear over a wider bias voltage range so that increased noise can enhance chaotic current oscillations in SSLs.…”

Enhancing chaotic behavior at room temperature in GaAs/(Al,Ga)As superlattices

“…Table I gives the numerical values of the parameters used in the simulations. The GaAs/Al 0.45 Ga 0.55 As configuration corresponds with the configuration used in experiments [10,18,23]. The rest of the parameters are as follows: l b and l w , with l = l b + l w , are the barrier and well lengths, respectively, and A = s 2 is the transversal area of the superlattice.…”