Electronic Devices and Semiconductors Quiz
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Questions and Answers

What are the two different types of material?

Resistance and Conductor

Why is the Semiconductor called intrinsic?

When no impurity is added

What is the process of adding impurities called?

Doping

What is the conductivity of a material proportional to?

<p>Concentration of free electrons</p> Signup and view all the answers

The number of free electrons in a semiconductor lies ______ to ______ electrons per cubic meter.

<p>10<sup>7</sup> to 10<sup>19</sup></p> Signup and view all the answers

Typically, semiconductors have a forbidden energy gap of about ______ eV.

<p>1</p> Signup and view all the answers

In a pure semiconductor, what is equal to the number of holes?

<p>Number of electrons</p> Signup and view all the answers

The holes and electrons move in the same direction in the field E.

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

The total current density (J) within the intrinsic semiconductor is given by J = ______ + ______

<p>Jn + Jp</p> Signup and view all the answers

Match the following symbols with their corresponding meanings:

<p>n = Number of electrons per unit volume p = Number of holes per unit volume E = Electric field strength q = Charge of an electron or hole</p> Signup and view all the answers

What does the symbol "n" represent?

<p>Number of electrons per unit volume</p> Signup and view all the answers

What is the meaning of the symbol E?

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

What is the formula for conductivity in terms of electron and hole mobility?

<p>σ = q(niMn + niMp)</p> Signup and view all the answers

What is the formula for "ni" in intrinsic semiconductors?

<p>ni = √(np)</p> Signup and view all the answers

What is the formula for conductivity of semiconductor in terms of intrinsic carrier concentration and mobility?

<p>σ = qni(μn + μp)</p> Signup and view all the answers

What is the value of mobility of free electrons in pure Germanium?

<p>3800 cm<sup>2</sup>/v.s</p> Signup and view all the answers

What is the value of mobility of holes in pure Germanium?

<p>1800 cm<sup>2</sup>/v.s</p> Signup and view all the answers

What is the intrinsic carrier concentration in Germanium?

<p>2.5 x 10<sup>13</sup> cm<sup>-3</sup></p> Signup and view all the answers

What is the value of mobility of free electrons in pure Silicon?

<p>1300 cm<sup>2</sup>/v.s</p> Signup and view all the answers

What is the value of mobility of holes in pure Silicon?

<p>500 cm<sup>2</sup>/v.s</p> Signup and view all the answers

What is the intrinsic carrier concentration in Silicon?

<p>1.5 x 10<sup>10</sup> cm<sup>-3</sup></p> Signup and view all the answers

What is the value for intrinsic conductivity of Germanium?

<p>2.7 x 10<sup>-8</sup> (Ω.m)<sup>-1</sup></p> Signup and view all the answers

What is the value for intrinsic conductivity of Silicon?

<p>4.32 x 10<sup>-4</sup> (Ω.m)<sup>-1</sup></p> Signup and view all the answers

What is the definition of a donor impurity?

<p>A pentavalent substituent atom that donates extra electrons to a semiconductor</p> Signup and view all the answers

What is the definition of an acceptor impurity?

<p>A trivalent substituent atom that creates a hole in a semiconductor</p> Signup and view all the answers

What is the definition of Fermi energy level?

<p>The energy level at which the probability of finding an electron is 50%</p> Signup and view all the answers

How does Fermi energy level help in separating electron and holes?

<p>It acts as an energy threshold separating occupied and unoccupied states in the semiconductor.</p> Signup and view all the answers

What is an energy band gap?

<p>The energy difference between the valence band and the conduction band.</p> Signup and view all the answers

How can we differentiate insulator, semiconductor, and conductor in terms of energy band gap?

<p>Insulators have a large band gap, semiconductors have a small band gap, and conductors have zero band gap.</p> Signup and view all the answers

How do we prepare n-type and p-type materials from an intrinsic semiconductor?

<p>By doping with donor and acceptor impurities respectively</p> Signup and view all the answers

What are the majority carriers in n-type semiconductor?

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

What is the most widely used semiconductor in electronic devices?

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

What is the energy gap between valence band and conduction band in conductors?

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

What is the range of visible light wavelength?

<p>400 nm to 700 nm</p> Signup and view all the answers

What is Plank's constant?

<p>6.626 x 10<sup>-34</sup> joule-second</p> Signup and view all the answers

What is the speed of light?

<p>3 x 10<sup>8</sup> meters per second</p> Signup and view all the answers

What is the relationship between energy and wavelength?

<p>They are inversely proportional</p> Signup and view all the answers

What is the formula for calculating energy band gap?

<p>Eb = hc/</p> Signup and view all the answers

What is the energy band gap of a material that emits light of 400 nm wavelength?

<p>3.12 eV</p> Signup and view all the answers

What is the definition of diffusion current?

<p>The current flow in a semiconductor due to a concentration gradient of charge carriers.</p> Signup and view all the answers

What is the formula for diffusion current density due to holes?

<p>Jp = -qDp(d(P)/dx)</p> Signup and view all the answers

What is the formula for diffusion current density due to electrons?

<p>Jn = qDn(d(n)/dx)</p> Signup and view all the answers

What is the definition of drift current?

<p>The current flow in a semiconductor due to an applied electric field.</p> Signup and view all the answers

What is the formula for drift current density due to electrons?

<p>Jne = qμnE</p> Signup and view all the answers

What is the formula for drift current density due to holes?

<p>Jph = qμpE</p> Signup and view all the answers

What is the formula for total current density in a semiconductor?

<p>J = (qDn(d(n)/dx) + qμnE) + (-qDp(d(P)/dx) + qμpE)</p> Signup and view all the answers

What is a PN junction diode?

<p>A two-terminal device that allows current to flow preferentially in one direction while blocking current in the other direction.</p> Signup and view all the answers

What is the formula for diode current?

<p>Id = Io(e^(V/nVT) - 1)</p> Signup and view all the answers

What is the formula for thermal voltage in a diode?

<p>VT = KT/q</p> Signup and view all the answers

Flashcards

Resistance

A material's opposition to the flow of electric current.

Conductor

A material that allows electric current to flow easily.

Semiconductor

A material with conductivity between that of a conductor and an insulator.

Silicon

A common semiconductor material.

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Intrinsic Semiconductor

A pure semiconductor with equal numbers of electrons and holes.

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Extrinsic Semiconductor

A semiconductor with added impurities to change its conductivity.

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Doping

Adding impurities to a semiconductor to change its electrical properties.

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n-type semiconductor

A semiconductor with extra electrons as charge carriers.

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p-type semiconductor

A semiconductor with extra holes as charge carriers.

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Thermal agitation

Random movement of atoms and electrons due to heat.

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Recombination

Meeting of electrons and holes that neutralizes them.

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Free electron

A negatively charged electron that is not bound to an atom.

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Hole

A vacancy in the electron structure (behaves as a positive charge).

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Mobility

The ability of charge carriers to move through a material.

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Current density

Current flowing through a specific area.

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Intrinsic conductivity (σ)

Measure of a pure semiconductor's conduction ability.

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Donor impurities

Impurities adding extra electrons to a semiconductor.

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Acceptor impurities

Impurities creating extra holes in a semiconductor.

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Energy band gap (Eg)

Energy difference between valence and conduction bands.

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Insulator

A material with a large energy gap, preventing current flow.

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Diffusion

Movement of particles due to concentration differences.

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PN Junction

Boundary between p-type and n-type semiconductors.

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Depletion region

Area near a PN junction with few charge carriers.

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Drift current

Current due to charge carriers moving under an electric field.

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What is conductivity of a material proportional to?

The conductivity of a material is directly proportional to the concentration of free electrons. This means more free electrons mean better conductivity.

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Semiconductor conductivity

Semiconductors have conductivity higher than insulators but lower than metals. This makes them useful for controlling current flow.

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Forbidden energy gap (Eg)

The energy difference between the valence band (where electrons are bound) and the conduction band (where electrons can move freely). Semiconductors have a small Eg, allowing electrons to jump between the bands with a little energy.

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Intrinsic Silicon

Pure silicon has an equal number of electrons and holes. This makes it a neutral semiconductor.

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Extrinsic Silicon

Silicon with added impurities to control its conductivity. This can be n-type (more electrons) or p-type (more holes).

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N-type impurity

Donor impurities (like phosphorus) add extra electrons to silicon, making it n-type. It's easier for current to flow due to the increased electrons.

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P-type impurity

Acceptor impurities (like boron) create holes in silicon, making it p-type. It's easier for current to flow due to the increased holes.

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Current density (J)

The amount of current flowing through a specific area. It's a measure of how concentrated the current is.

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Donor and Acceptor impurities

Impurities added to semiconductors to change their conductivity. Donors add extra electrons (n-type), while acceptors create holes (p-type).

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Energy band structure

Describes how electrons are arranged in energy levels within a material. It determines whether a material is an insulator, semiconductor or conductor.

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Forward Bias

When a voltage is applied across a diode in a way that allows current to flow easily. This happens when the positive terminal of the battery is connected to the p-type side and the negative terminal is connected to the n-type side.

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Reverse Bias

When a voltage is applied across a diode in a way that blocks current flow. This happens when the negative terminal of the battery is connected to the p-type side and the positive terminal is connected to the n-type side.

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Reverse Saturation Current (Io)

The small current that flows through a diode when it's reverse biased. It's typically very small.

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Forward Current (If)

The current that flows through a diode when it's forward biased. It's typically large.

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PN Junction Diode

A device made by joining p-type and n-type semiconductors. It acts like a one-way gate for current, allowing it to flow easily in one direction and hardly at all in the other.

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Study Notes

Electronic Devices

  • Different types of materials:

    • Conductors: Current flows easily
    • Insulators: Current cannot flow easily
    • Semiconductors: Current flows with more difficulty than a conductor but easier than an insulator

  • Semiconductors:

    • Conductivity is proportional to the concentration of free electrons
    • Number of free electrons in a semiconductor is between 10^7 and 10^18 electrons/m^2
    • Typically has a forbidden energy gap of approximately 1 eV

  • Doping:

    • Adding impurities to semiconductors
    • Creates extrinsic semiconductors

Conductivity of Silicon

  • Intrinsic Silicon: n = p
  • Mobility is a crucial element influencing conductivity
  • Conductivity in a semiconductor depends on the concentration of charge carriers (holes and electrons) and their individual mobilities

Conductivity of Semiconductor

  • In a pure semiconductor, the number of holes equals the number of electrons

  • Thermal agitation continuously creates electron-hole pairs

  • Electron-hole pairs recombine

  • The total current density in an intrinsic semiconductor (J) is given by

    • J = Jn + Jp, where Jn and Jp are the current densities due to electrons and holes, respectively
    • Jn = q * n * μn * E, where q is the charge, n is the electron concentration, μn is the electron mobility, and E is the electric field
    • Jp = q * p * μp * E, where p is the hole concentration, and μp is the hole mobility

Resistivity

  • Resistivity (ρ) is the reciprocal of conductivity (σ), ρ = 1/σ
  • Resistivity equation: ρ = 1/(q(n * μn + p * μp))

Donor and Acceptor impurities

  • Pentavalent impurities: Donate extra electrons - n-type impurities
  • Trivalent impurities: Create holes - p-type impurities

Energy Band Structures and Conduction in Insulators, Semiconductors, and Conductors

  • Energy gaps differentiate these materials
    • Insulators have a large energy gap (Eg > 4 eV)
    • Conductors have a small energy gap (Eg < 1 eV)
    • Semiconductors have an intermediate energy gap (Eg ~ 1 eV)

Drift and Diffusion

  • Diffusion: Movement of particles due to a concentration gradient.
  • Drift: Movement of particles due to an electric field

Questions

  • Band gap: Differentiates insulators, semiconductors, and conductors
  • Preparation of n-type and p-type materials: Adding impurities to intrinsic semiconductors creates n-type (extra electrons) and p-type (holes) materials
  • Intrinsic conductivity: Mobility of electrons and holes impacts conductivity
  • Fermi-energy level: Separates electrons and holes
  • Donor/Acceptor impurities: Introduce extra electrons/holes, respectively
  • Importance of band gap: Determines the material's electrical properties

Special Diodes

  • Zener diode: Operates in the breakdown region for voltage regulation
  • Schottky diode: Unipolar device, fast switching

Solar Cell

  • Generates DC voltage - converts light energy to electrical energy

Bipolar Junction Transistor (BJT)

  • Common base configuration: IE = Ic + IB
  • Active region: Current amplification
  • Saturation region: Current almost constant
  • Cut-off region: Current very low

Field Effect Transistor (FET)

  • N-channel JFET: Majority carriers are electrons
  • P-channel JFET: Majority carriers are holes
  • Types of FETs: JFET, MOSFET
  • FET operation: Controlled by an electric field

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Electronic Devices PDF

Description

Test your understanding of electronic devices, focusing on conductors, insulators, and semiconductors. Explore key concepts such as doping, intrinsic and extrinsic semiconductors, and the conductivity of silicon. This quiz will challenge your knowledge on the properties and behavior of semiconductor materials.

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