Hyperchaos, intermittency, noise and disorder in modified semiconductor superlattices

TL;DR

This paper models nonlinear semiconductor superlattices, revealing how noise and disorder influence complex phenomena like hyperchaos and intermittency, with implications for device applications and understanding of electron transport.

Contribution

It introduces a comprehensive sequential transport model that incorporates noise and disorder effects, analyzing their impact on chaos and excitability in superlattices.

Findings

Hyperchaos occurs over extended voltage ranges.

Disorder due to growth fluctuations can suppress chaos.

More than 70% of samples remain chaotic below certain disorder levels.

Abstract

Weakly coupled semiconductor superlattices under dc voltage bias are nonlinear systems with many degrees of freedom whose nonlinearity is due to sequential tunneling of electrons. They may exhibit spontaneous chaos at room temperature and act as fast physical random number generator devices. Here we present a general sequential transport model with different voltage drops at quantum wells and barriers that includes noise and fluctuations due to the superlattice epitaxial growth. Excitability and oscillations of the current in superlattices with identical periods are due to nucleation and motion of charge dipole waves that form at the emitter contact when the current drops below a critical value. Insertion of wider wells increases superlattice excitability by allowing wave nucleation at the modified wells and more complex dynamics. Then hyperchaos and different types of intermittent chaos are possible on extended dc voltage ranges. Intrinsic shot and thermal noises and external noises produce minor effects on chaotic attractors. However, random disorder due to growth fluctuations may suppress any regular or chaotic current oscillations. Numerical simulations show that more than 70\% of samples remain chaotic when the standard deviation of their fluctuations due to epitaxial growth is below 0.024 nm (10\% of a single monolayer) whereas for 0.015 nm disorder suppresses chaos.