Semiconductor Physics Lecture: Semiconductors and Light
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Questions and Answers

What type of materials contain large densities of free electrons, leading to a strong contribution to the dielectric function?

  • Metals and lightly doped semiconductors
  • WTO Al2O3 materials
  • Metals and heavily doped semiconductors (correct)
  • Optical media and insulators
  • In a free electron plasma, what happens when the free electrons interact with electromagnetic radiation?

  • They exhibit a strong restoring force
  • They behave like atomic oscillators
  • They experience a zero restoring force (correct)
  • Their polarization is independent of the electric field
  • What formula can be used to calculate the dielectric function of a metal or a doped semiconductor?

  • Atomic oscillator formula
  • Plasma frequency formula
  • Clausius-Mosotti formula
  • Drude-Lorentz formula (correct)
  • In an ideal metal with zero damping, what is the behavior of the plasma frequency?

    <p>It remains constant</p> Signup and view all the answers

    Why are metals transparent in the UV region?

    <p>They absorb UV light efficiently</p> Signup and view all the answers

    What characterizes the dielectric function of a free electron plasma?

    <p>It contains a plasma frequency term</p> Signup and view all the answers

    What induces a current density J in a metal during a time-varying field?

    <p>Finite AC electrical conductivity</p> Signup and view all the answers

    In the equation of motion for free electron plasma, what does the symbol 'g' represent?

    <p>Reciprocal of the characteristic timescale</p> Signup and view all the answers

    What is the relationship between momentum scattering time and momentum loss in free electron plasma?

    <p>Inversely proportional</p> Signup and view all the answers

    How does the velocity v(t) in free electron plasma behave with respect to time?

    <p>Has a harmonic time dependence</p> Signup and view all the answers

    What does the dielectric function of a free electron plasma represent?

    <p>AC conductivity measurements</p> Signup and view all the answers

    Which term in the equation Ne 2 / s(w) represents the AC conductivity in free electron plasma?

    <p>(1/t - iw)</p> Signup and view all the answers

    What type of transitions occur in semiconductors during inter-band transitions?

    <p>Valence Band to Conducting Band transitions</p> Signup and view all the answers

    How can mid-bandgap states in wide bandgap materials be created for optical activity?

    <p>Adding impurities</p> Signup and view all the answers

    What gives metals their characteristic shiny appearance?

    <p>Free electron interactions with light</p> Signup and view all the answers

    In which part of the spectrum does free carrier absorption typically occur in semiconductors?

    <p>Infrared (IR)</p> Signup and view all the answers

    What is a common method to introduce 'Colour centres' in materials like sapphire?

    <p>Ion beam or X-ray irradiation</p> Signup and view all the answers

    What is a characteristic feature of the optical response of all insulators and semiconductors?

    <p>A very characteristic form in T(E)</p> Signup and view all the answers

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