Multistability, chaos, and random signal generation in semiconductor superlattices

Area of Science:

• Solid State Physics
• Nonlinear Dynamics
• Quantum Electronics

Background:

• Semiconductor superlattices are engineered periodic structures designed to manipulate electronic properties.
• These structures hold potential for generating radiation in the subterahertz and terahertz (THz) range, addressing the 'THz gap'.
• Previous research indicated chaotic dynamics in superlattices, suggesting applications in THz random signal generation.

Purpose of the Study:

• To investigate the nonlinear dynamics of hot electrons in semiconductor superlattices under external electrical driving.
• To explore the role of multistability in hindering reliable chaos-based random signal generation.
• To demonstrate a method for eliminating multistability and achieving robust chaos for THz applications.

Main Methods:

• Modeling hot electron dynamics in semiconductor superlattices, including space charge effects.
• Systematic phase space exploration to identify chaotic and regular dynamics.
• Analysis of system behavior under single-frequency and quasiperiodic (incommensurate frequency) driving fields.

Main Results:

• Single-frequency driving typically leads to multistability, where both chaotic and regular motions coexist.
• The transition to multistability with chaos was found to be abrupt.
• Applying a second, incommensurate driving frequency successfully eliminated multistability, making chaos the sole asymptotic behavior.

Conclusions:

• Multistability in semiconductor superlattices impedes their use as reliable random signal sources.
• Quasiperiodic driving of semiconductor superlattices can eliminate multistability, enabling predictable access to chaotic attractors.
• This approach offers a promising pathway for developing robust random signal generators to address the THz gap.