EEPC13 Electron Devices Quiz
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Questions and Answers

What is the bandgap energy for silicon?

  • 0.67 eV
  • 1.43 eV
  • 2.5 eV
  • 1.12 eV (correct)

    • Which of the following statements about semiconductors is correct?

  • Semiconductors can tailor conductivity, unlike metals and insulators. (correct)
  • Semiconductors cannot be used in electronic devices.
  • Semiconductors have the same properties as metals at any temperature.
  • Semiconductors always have a bandgap energy greater than 2.5 eV.

    • Which group of elements listed contains semiconductors with suitable bandgap energies for electronic uses?

  • Noble gases
  • Alkaline earth metals
  • Metalloids like silicon and germanium (correct)
  • Transition metals

    • What does Moore's Law state about integrated circuits (ICs)?

    <p>The number of transistors in an IC chip doubles approximately every two years.</p> Signup and view all the answers

    What is the effect of bringing silicon atoms close together?

    <p>They create a continuum of energy states.</p> Signup and view all the answers

    What is the primary characteristic of semiconductors?

    <p>Their conductivity lies between that of insulators and conductors.</p> Signup and view all the answers

    Which of the following elements has the highest number of valence electrons?

    <p>Neon</p> Signup and view all the answers

    According to the Bohr model, how many electrons can exist in the second shell?

    <p>8</p> Signup and view all the answers

    What happens to the resistivity of a semiconductor at absolute zero temperature?

    <p>It becomes equal to that of an insulator.</p> Signup and view all the answers

    What is the outermost shell of an atom known as?

    <p>Valence shell</p> Signup and view all the answers

    Which material represents the best conductors?

    <p>Silver</p> Signup and view all the answers

    What does the term 'valence electron' refer to?

    <p>Electrons in the valence shell.</p> Signup and view all the answers

    How does the energy level change from the first shell to the valence shell?

    <p>It increases.</p> Signup and view all the answers

    What is the maximum number of electrons that can occupy the p sublevel?

    <p>6</p> Signup and view all the answers

    Which statement correctly explains the behavior of silicon at absolute zero temperature?

    <p>Silicon behaves as an insulator.</p> Signup and view all the answers

    According to the diagonal rule, which of the following electron configurations is correct for sulfur?

    <p>1S² 2S² 2P⁶ 3S² 3P⁴</p> Signup and view all the answers

    What defines the spacing between two neighbouring atoms in a crystal structure?

    <p>Lattice constant</p> Signup and view all the answers

    What occurs when an electron breaks free from its covalent bond in silicon?

    <p>A hole is created.</p> Signup and view all the answers

    In relation to energy levels, how many total sublevels would be present at energy level n=4?

    <p>4</p> Signup and view all the answers

    What type of bond is formed when silicon atoms share valence electrons?

    <p>Covalent bond</p> Signup and view all the answers

    What is the total number of orbitals in a d sublevel?

    <p>5</p> Signup and view all the answers

    What is the relationship between the energy levels of conduction band (Ec) and valence band (Ev) in a semiconductor?

    <p>Eg = Ec - Ev</p> Signup and view all the answers

    What factor primarily determines the intrinsic carrier concentration (ni) in silicon at a given temperature?

    <p>The band gap energy (Eg)</p> Signup and view all the answers

    At room temperature (300K), how does the number of free electrons in intrinsic silicon compare to the number of silicon atoms?

    <p>There is a very low number of free electrons compared to silicon atoms</p> Signup and view all the answers

    What is the density of free electrons (ni) in intrinsic silicon at room temperature based on the given formula?

    <p>$1.5 \times 10^{10}$ electrons/cm³</p> Signup and view all the answers

    Why do holes move slower than electrons in silicon?

    <p>Electron mobility is greater than hole mobility</p> Signup and view all the answers

    What is the forbidden band gap energy (Eg) range for insulators?

    <p>3 to 6 eV</p> Signup and view all the answers

    In intrinsic semiconductors, what is the relationship between the density of free electrons and the density of holes?

    <p>Density of free electrons equals density of holes</p> Signup and view all the answers

    How is the density of holes (P) represented mathematically in relation to intrinsic carrier density (ni)?

    <p>P = ni</p> Signup and view all the answers

    What is the intrinsic carrier concentration formula used for calculating properties in semiconductors?

    <p>Ni = BT^3/2 e^-Eg/KT</p> Signup and view all the answers

    Which element acts as a dopant to form n-type semiconductors?

    <p>Phosphorus (P)</p> Signup and view all the answers

    Which of the following is an example of a trivalent impurity used to create p-type semiconductors?

    <p>Boron (B)</p> Signup and view all the answers

    At room temperature, which energy level do free electrons in an n-type semiconductor generally occupy?

    <p>Conduction Band</p> Signup and view all the answers

    What is the value of the band gap energy (Eg) for Gallium Arsenide (GaAs)?

    <p>1.4 eV</p> Signup and view all the answers

    What describes the influence of the nucleus on a free electron in an n-type semiconductor?

    <p>Electrons are partially confined.</p> Signup and view all the answers

    What is the consequence of doping silicon with trivalent elements?

    <p>It causes empty states or holes.</p> Signup and view all the answers

    When phosphorus atoms are introduced into silicon, what is the result?

    <p>It adds more free electrons.</p> Signup and view all the answers

    What is the expression for the velocity vector of electrons in an electric field?

    <p>vë = -MnẺ</p> Signup and view all the answers

    How is the total current density J for a semiconductor defined in the given content?

    <p>J = q(Mn.n + Mp.p)DE</p> Signup and view all the answers

    What happens to the velocity of charge carriers at high electric fields according to the content?

    <p>Velocity becomes constant and reaches a saturation level.</p> Signup and view all the answers

    Which of the following mobility values is correct for holes in silicon?

    <p>480 cm²/Vs</p> Signup and view all the answers

    What is the main physical phenomenon responsible for the decrease in velocity of electrons as they accelerate in a semiconductor?

    <p>Collisions with lattice atoms.</p> Signup and view all the answers

    Study Notes

    EEPC13 Electron Devices

    • Reference Textbooks:
      • Electronic Devices and Circuits - David A Bell, PHI
      • Electronic Devices and Circuits - Milman and Halkias, McGraw-Hill
      • Electronic Devices and ckt theory - Boylestad
      • Fundamentals of Microelectronics - Behzad Razavi

    Basic Concepts of Semiconductors

    • Semiconductors are elements with conductivity between a good conductor and an insulator.
    • Types of Semiconductors:
      • Single Crystal (Ge, Si): Have a repetitive crystal structure.
      • Compound:
        • GaAs (Gallium Arsenide)
        • CdS (Cadmium Sulfide)
        • GaN (Galium Nitride)
        • GaAsP (Gallium Arsenide Phosphide)

    Atomic Structure

    • Matter is composed of atoms consisting of electrons, protons, and neutrons (except normal hydrogen which has no neutrons).
    • Bohr Model: Atoms have a nucleus (containing protons and neutrons) and electrons orbiting the nucleus.
    • Quantum Model: A more accurate model of the atom but more complex to visualize.
    • Atomic Number: The number of protons in the nucleus.
    • Maximum Number of Electrons per Shell:
      • The maximum number of electrons that can occupy a shell is given by 2n², where n is the shell number (e.g., n=1, 2, 3...).
    • Valence Shell: The outermost electron shell of an atom. Atoms with 8 electrons in the valence shell are typically more stable (neon).
    • Valence Electrons: Electrons in the valence shell; their number influences whether a material is a conductor, insulator, or semiconductor.

    Solids, Insulators, Conductors, and Semiconductors

    • Solids: Atoms are closely packed in a periodic arrangement called a lattice structure.
    • Insulators: Have 8 valence electrons and high band gaps.
    • Conductors: Have low valence electron counts (<4), low band gaps, and allow easy electron flow.
    • Semiconductors: Have 4 valence electrons and moderate band gaps. Their conductivity lies between those of insulators and conductors. At absolute zero conductivity is equivalent to an insulator, with higher conductivity as temperature increases.

    Energy Levels

    • Energy levels within an atom are discrete (the energy levels we have are not continuously possible).
    • Sublevels (s, p, d, f): Electrons can have different energy levels with in each energy level (e.g. s, p, d, f).
    • Each sublevel corresponds to a maximum number of electrons that can occupy it.
    • Atomic orbitals: Each sublevel has one or more orbitals which can maximally contain 2 electrons.
    • Diagonal Rule for electron filling: Describes the order in which electrons fill orbitals and sublevels in atoms.

    Band Gap Energy

    • The energy difference between the valence band and the conduction band in a material.
    • Different materials with varying bandgaps dictate whether that material behaves as a semiconductor, conductor, or insulator.
    • Insulators have a large band gap in comparison to semiconductors or conductors.

    Doping

    • Controlled addition of impurities to an intrinsic semiconductor material.
    • Creates either n-type or p-type semiconductors.
    • Extrinsic semiconductors: More than one type of dopant exists.
    • N-type Semiconductors: Pentavalent impurities (having 5 valence electrons) increase concentration of free electrons
    • P-type Semiconductors: Trivalent impurities (having 3 valence electrons) increase the concentration of holes (absence of electrons).

    Carrier Transport

    • Drift: The movement of charge carriers in response to an electric field.
    • Diffusion: The movement of charge carriers due to differences in concentration.
    • Current Density: Current flowing per unit area.
    • Mobility: The measure of how easily charge carriers move in response to an electric field.

    The Mass Action Law

    • The product of the electron density and hole density in an intrinsic semiconductor remains constant. 
    • Doping changes electron and hole concentrations.

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    EEPC13 Electron Devices Lecture Notes PDF

    Description

    Test your knowledge on electron devices and the fundamental concepts of semiconductors. This quiz covers semiconductor types, atomic structure, and key models like Bohr and Quantum. Review important topics from various reference textbooks to prepare effectively.

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