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Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
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Carrier generation is the process by which electron-hole pairs (EHPs) are created within the semiconductor. In direct-bandgap semiconductors, such as gallium arsenide (GaAs), this occurs efficiently when energy absorption prompts valence electrons to leap into the conduction band, leaving behind holes.
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The vacuum level denotes the energy threshold required for an electron to escape from a material surface. It is usually positioned above the conduction band of a semiconductor and acts as a benchmark for comparing electron energies within various materials.
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Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
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An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure of the strength of this attraction. The lattice energy (ΔHlattice) of an ionic compound is defined as the energy required to separate one mole of the solid into its component gaseous ions. For the ionic solid sodium chloride, the lattice energy is the enthalpy change of the process:
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Hyperchaos, Intermittency, Noise and Disorder in Modified Semiconductor Superlattices.

Luis L Bonilla1,2, Manuel Carretero1,2, Emanuel Mompó1,3

  • 1Gregorio Millán Institute for Fluid Dynamics, Nanoscience and Industrial Mathematics, Universidad Carlos III de Madrid, 28911 Leganés, Spain.

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Semiconductor superlattices exhibit chaos and current oscillations due to electron tunneling. Disorder from growth fluctuations can suppress these effects, impacting their use as random number generators.

Keywords:
chaoschaos designchaotic devicesfast true random number generatorsfluctuationshyperchaosintermittencynonlinear electron transportsecure communicationssemiconductor superlattices

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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.