Semiconductor Electronics Overview
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Questions and Answers

What happens to the resistance of a semiconductor as temperature increases?

  • Resistance remains constant.
  • Resistance decreases. (correct)
  • Resistance increases.
  • Resistance fluctuates unpredictably.

    • Which semiconductor type refers to pure material with no doping?

  • Conduction semiconductor
  • Extrinsic semiconductor
  • Valence semiconductor
  • Intrinsic semiconductor (correct)

    • Which statement about the energy band gaps of carbon, silicon, and germanium is correct?

  • (Eg)Si < (Eg)Ge < (Eg)C
  • (Eg)C > (Eg)Si > (Eg)Ge (correct)
  • (Eg)C < (Eg)Si > (Eg)Ge
  • (Eg)C = (Eg)Si = (Eg)Ge

    • What occurs when electrons in the valence band cross the energy gap?

    <p>They gain energy and enter the conduction band.</p> Signup and view all the answers

    What is referred to as a 'hole' in semiconductor physics?

    <p>A vacancy in the valence band with a positive charge.</p> Signup and view all the answers

    Which factor primarily determines the conductivity of semiconductors?

    <p>Temperature and electron mobility</p> Signup and view all the answers

    What effect does temperature have on the number of charge carriers in a semiconductor?

    <p>Increases the number of free electrons and holes.</p> Signup and view all the answers

    In which scenario would an extrinsic semiconductor be used?

    <p>To modify electrical properties using impurities.</p> Signup and view all the answers

    What characterizes the conduction band in conductors?

    <p>The conduction band is partially filled.</p> Signup and view all the answers

    What does the energy gap between the valence band and the conduction band represent?

    <p>The energy required to move electrons from the valence band to the conduction band.</p> Signup and view all the answers

    How does the nature of electron motion in a solid compare to that in an isolated atom?

    <p>Electrons in solids have overlapping orbits.</p> Signup and view all the answers

    What is meant by continuous energy variations within energy bands?

    <p>Each electron is affected by a unique pattern of surrounding charges.</p> Signup and view all the answers

    Which type of material has an empty conduction band?

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

    What is the characteristic of the valence band in conducting materials?

    <p>It is partially filled with electrons that can easily move.</p> Signup and view all the answers

    What occurs when atoms come close together to form a solid?

    <p>Electrons can share energy levels with neighboring atoms.</p> Signup and view all the answers

    What defines the conduction band in semiconductors?

    <p>It is typically partially filled and can contain free electrons.</p> Signup and view all the answers

    What happens to holes in the p-region of an unbiased p-n junction?

    <p>They diffuse into the n-region.</p> Signup and view all the answers

    What is the term used for the motion of minority charge carriers due to an electric field in a p-n junction?

    <p>Drift current</p> Signup and view all the answers

    Under equilibrium in a p-n junction, what happens to the net current?

    <p>The net current becomes zero.</p> Signup and view all the answers

    What primarily initiates the drift current in a p-n junction?

    <p>Electric field development</p> Signup and view all the answers

    In the context of p-n junctions, what does 'diffusion current' refer to?

    <p>Movement of charge carriers from high concentration to low concentration.</p> Signup and view all the answers

    When an external voltage is applied to a p-n junction, what happens to the direction of current?

    <p>It flows in the same direction as the applied voltage.</p> Signup and view all the answers

    What role do metallic contacts play in a semiconductor diode?

    <p>They allow for current to enter and exit the diode.</p> Signup and view all the answers

    What causes the drift current to become significant in a p-n junction over time?

    <p>Expansion of the depletion region.</p> Signup and view all the answers

    In a p-type semiconductor, which particles are considered the majority carriers?

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

    What type of impurities are used to create p-type semiconductors?

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

    What is the relationship between additional charge carriers and the ionized cores in n-type and p-type semiconductors?

    <p>They are equal in charge.</p> Signup and view all the answers

    Which element is mentioned as having an energy gap of 0 eV?

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

    What is the energy gap of silicon as indicated in the content?

    <p>1.1 eV</p> Signup and view all the answers

    How does the energy gap vary between diamond, silicon, and germanium?

    <p>Diamond &gt; Silicon &gt; Germanium</p> Signup and view all the answers

    What happens to a pure silicon crystal when it is doped with trivalent impurities?

    <p>It becomes p-type.</p> Signup and view all the answers

    Which material has the smallest energy gap among diamond, silicon, and germanium?

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

    What occurs when the reverse voltage reaches the breakdown voltage (Vbr) in a diode?

    <p>The reverse current increases sharply.</p> Signup and view all the answers

    Which statement correctly explains the behavior of reverse current in a diode until the breakdown voltage is reached?

    <p>Reverse current is independent of reverse voltage up to a critical value.</p> Signup and view all the answers

    What is the function of a diode when used as a rectifier?

    <p>It converts alternating current to direct current.</p> Signup and view all the answers

    What effect does reverse bias have on the majority carriers in a diode?

    <p>It reduces the number of majority carriers reaching the junction.</p> Signup and view all the answers

    To calculate the resistance of a diode at specific operating points, what parameters are required?

    <p>Both the current and the voltage at the specified operating points.</p> Signup and view all the answers

    What is the approximate order of drift current in diodes?

    <p>A few µA</p> Signup and view all the answers

    In forward bias, what happens when the voltage reaches a certain threshold?

    <p>The diode current increases significantly.</p> Signup and view all the answers

    What is the cutoff voltage for silicon diodes typically around?

    <p>0.7 V</p> Signup and view all the answers

    What happens to the current in reverse bias when a voltage is applied?

    <p>It is constant and very small.</p> Signup and view all the answers

    How is dynamic resistance defined in the context of a diode?

    <p>As the ratio of small change in voltage to small change in current.</p> Signup and view all the answers

    What type of ammeter is used to measure current in reverse bias conditions?

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

    What is a characteristic feature of a silicon diode's I-V curve in forward bias?

    <p>Current increases rapidly after reaching a threshold voltage.</p> Signup and view all the answers

    Signup and view all the answers

    Study Notes

    Semiconductor Electronics

    • Atomic Model and Solids: Electrons in isolated atoms have specific energy levels determined by their orbits. In solids, atoms are close together, and electron orbits overlap. This leads to different electron behavior in a solid compared to an isolated atom.

    Energy Bands

    • Energy Levels in Crystals: Each electron in a crystal has a unique energy level, differing from others due to surrounding charges.
    • Energy Bands: These unique energy levels combine to form continuous energy bands, replacing distinct energy levels.
    • Valence Band & Conduction Band: The valence band contains electrons involved in bonding, the conduction band lets electrons move freely. A gap (Energy gap, Eg) separates these bands.

    Energy Bands in Conductors, Semiconductors and Insulators

    • Conductors: Valence and conduction bands overlap (or the conduction band is partially filled) resulting in low resistance.
    • Semiconductors: A small band gap exists between valence and conduction bands. At room temperature, some electrons gain energy and jump from valence to conduction band, increasing conductivity.
    • Insulators: A large band gap exists, hindering electron movement to the conduction band, leading to high resistance.

    Semiconductors

    • Insulators: Large band gaps, no conduction at room temperature.
    • Semiconductors: Moderate band gaps. Room temperature allows some electrons to move to the conduction band. Conductivity increases with temperature.
    • Doping: Adding specific impurities (dopants) to semiconductors adjusts their conductivity and creates n-type or p-type semiconductors.
    • n-type: Pentavalent impurities add extra electrons. (Majority carries are electrons, Minority carriers are holes).
    • p-type: Trivalent impurities create "holes" which act like positive charge carriers. (Majority carries are holes, Minority carriers are electrons).
    • Intrinsic Semiconductors: Pure, undoped semiconductors.
    • Extrinsic Semiconductors: Doped semiconductors (n-type or p-type).

    p-n Junction

    • Formation: A p-n junction arises from the boundary between p-type and n-type semiconductors.
    • Diffusion: Holes diffuse from the p-side to the n-side, and electrons from the n-side to the p-side.
    • Depletion Region: This region near the junction develops a negative charge on the n-side and positive charge on the p-side preventing further diffusion.
    • Potential Barrier: A potential difference builds up across the depletion region.
    • p-n junction diode: A p-n junction with external contacts.
    • Forward bias: Voltage applied across the junction which reduces the depletion layer and allows current flow.
    • Reverse bias: Voltage applied across the junction which increases the depletion layer width and thus reducing current flow.
    • I-V characteristics: This illustrates how diode current changes with voltage.

    Rectifiers

    • Half-Wave Rectifier: Allows current flow during only one half of the AC cycle.
    • Full-Wave Rectifier: Allows current flow during both half of the AC cycle, resulting in smoother DC output.
      • Uses a center-tapped transformer.

    Filters

    • Capacitor Filters: Smooth out the ripple in the rectified DC output.
    • Inductor Filters: Used to block high frequency AC components.

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    Semiconductor Electronics: Materials, Devices and Simple Circuits PDF

    Description

    Explore the fundamentals of semiconductor electronics, focusing on atomic models, energy bands, and the differences between conductors, semiconductors, and insulators. This quiz covers key concepts such as energy levels, valence and conduction bands, and their implications in electronic materials.

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