Hyperchaos, Intermittency, Noise and Disorder in Modified Semiconductor Superlattices

Area of Science:

• Condensed Matter Physics
• Nonlinear Dynamics
• Semiconductor Devices

Background:

• Weakly coupled semiconductor superlattices are nonlinear systems exhibiting complex dynamics.
• Sequential tunneling of electrons is the primary source of nonlinearity.
• These systems can display spontaneous chaos at room temperature, suggesting potential as random number generators.

Purpose of the Study:

• To present a general sequential transport model for semiconductor superlattices.
• To investigate the influence of varying voltage drops, noise, and epitaxial growth fluctuations on system dynamics.
• To explore the conditions leading to excitability, oscillations, and different types of chaos.

Main Methods:

• Development of a general sequential transport model incorporating differential voltage drops across wells and barriers.
• Inclusion of noise and fluctuations arising from epitaxial growth imperfections.
• Numerical simulations to analyze current oscillations, excitability, and chaotic behaviors like hyperchaos and intermittent chaos.

Main Results:

• Excitability and current oscillations arise from charge dipole wave nucleation and motion below a critical current.
• Wider wells enhance excitability and lead to more complex dynamics, including hyperchaos and intermittent chaos.
• Disorder from epitaxial growth fluctuations can suppress oscillations; chaos persists in over 70% of samples with fluctuations below 0.024 nm standard deviation.

Conclusions:

• Semiconductor superlattices exhibit rich nonlinear dynamics, including chaos and current oscillations, driven by sequential tunneling.
• Epitaxial growth disorder significantly impacts these dynamics, potentially suppressing chaos, with a critical fluctuation level identified.
• The findings are crucial for understanding and optimizing semiconductor superlattices for applications such as fast physical random number generators.