Semiconductor Electronics: Devices and Materials
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Questions and Answers

What happens to electrons in intrinsic semiconductors as the temperature increases?

  • They become more tightly bound to the nucleus.
  • They lose their charge.
  • They completely fill the valence band.
  • They may acquire enough energy to break free from the covalent bonds. (correct)

In intrinsic semiconductors, the number of free electrons is not equal to the number of holes.

False (B)

What are the two most common intrinsic semiconductors mentioned?

Silicon (Si) and Germanium (Ge)

As the temperature rises in an intrinsic semiconductor, thermal energy can ionize some atoms, creating ________ which are positively charged particles.

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

Match the following terms with their definitions:

<p>Valence Bond = A shared electron pair between atoms in a covalent bond Free Electron = An electron that has broken away from its covalent bond Hole = A vacancy left behind by a free electron with positive charge Intrinsic Semiconductor = A pure semiconductor with equal amounts of free electrons and holes</p> Signup and view all the answers

Which of the following materials is an example of an elemental semiconductor?

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

Insulators have high conductivity compared to metals.

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

Name two types of compounds that can be considered as compound semiconductors.

<p>Inorganic and Organic</p> Signup and view all the answers

The conductivity of semiconductors is intermediate to _____ and _____ .

<p>metals, insulators</p> Signup and view all the answers

Match the following semiconductor types with their examples:

<p>Elemental Semiconductors = Silicon Inorganic Compound Semiconductors = Gallium Arsenide Organic Semiconductors = Polypyrrole Organic Polymer Semiconductors = Doped Pthalocyanines</p> Signup and view all the answers

Which of the following is NOT a characteristic of metals?

<p>Intermediate conductivity (C)</p> Signup and view all the answers

All semiconductor materials can be categorized as either elemental or compound.

<p>True (A)</p> Signup and view all the answers

What is the resistivity range of semiconductors?

<p>Approximately $10^{-5} - 10^{6} ext{ } ext{W m}$</p> Signup and view all the answers

What is the primary function of a vacuum tube in electronics?

<p>Controlled flow of electrons (A)</p> Signup and view all the answers

Semiconductor devices require an evacuated space to operate effectively.

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

What are the two electrodes in a vacuum diode called?

<p>Anode and Cathode</p> Signup and view all the answers

Semiconductor devices are generally _____ in size compared to vacuum tubes.

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

Match the following vacuum tube types with their number of electrodes:

<p>Diode = 2 Triode = 3 Tetrode = 4 Pentode = 5</p> Signup and view all the answers

Which of the following is NOT a characteristic of semiconductor devices?

<p>Operate at high voltages (D)</p> Signup and view all the answers

Light and heat have no effect on the flow of charge carriers in semiconductor devices.

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

What kind of devices were used before the invention of the transistor?

<p>Vacuum tubes</p> Signup and view all the answers

A _______ circuit can be formed using semiconductor devices for electronic applications.

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

Which feature makes semiconductor devices more favorable than vacuum tubes?

<p>Low power consumption (C)</p> Signup and view all the answers

Which elemental semiconductors are primarily discussed in this context?

<p>Si and Ge (D)</p> Signup and view all the answers

The conduction band is normally filled with electrons under standard conditions.

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

What happens to the energy levels of electrons when atoms form a solid?

<p>They form energy bands due to overlapping or close outer orbits.</p> Signup and view all the answers

The band above the valence band, where electrons can move freely if populated, is called the __________.

<p>conduction band</p> Signup and view all the answers

Which of the following describes a key characteristic of metallic conductors?

<p>Overlapped valence and conduction bands (C)</p> Signup and view all the answers

Organic semiconductors were developed before elemental semiconductors.

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

What is the significance of the gap between the valence band and conduction band?

<p>It determines whether electrons can move freely; a gap means electrons cannot move.</p> Signup and view all the answers

The electrons from the valence band can move to the conduction band if there is __________ between them.

<p>no gap or an overlap</p> Signup and view all the answers

In what year did organic semiconductors start becoming relevant?

<p>1990 (C)</p> Signup and view all the answers

What is the energy gap (Eg) for semiconductors?

<p>0.2 eV to 3 eV (D)</p> Signup and view all the answers

The p-n junction is not important for semiconductor devices.

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

What is the effect of forward bias on the junction barrier in a p-n junction?

<p>The barrier decreases.</p> Signup and view all the answers

In insulators, the energy gap (Eg) is greater than ______.

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

What is formed at a p-n junction?

<p>A depletion layer (A)</p> Signup and view all the answers

Electrons can be excited from the valence band to the conduction band only by heat.

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

What happens to the current flowing in a semiconductor when electrons are excited to the conduction band?

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

Match the following terms with their corresponding descriptions:

<p>p-type semiconductor = Doped with acceptor atoms n-type semiconductor = Doped with donor atoms depletion layer = Region with immobile ion-cores junction potential barrier = Energy barrier at p-n junction</p> Signup and view all the answers

What is the role of a diode in electrical circuits?

<p>Rectifying alternating current</p> Signup and view all the answers

In elemental semiconductors, n-type and p-type materials are created by introducing ______.

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

Flashcards

Semiconductors

Materials with conductivity between metals and insulators, typically used in electronic devices.

Elemental Semiconductors

Silicon (Si) and Germanium (Ge) are the most common, used in transistors, diodes, and integrated circuits.

Compound Semiconductors

Compounds like Cadmium Sulphide (CdS), Gallium Arsenide (GaAs), and Indium Phosphide (InP) are used in specialized applications like lasers and solar cells.

Insulators

Materials with extremely low conductivity, preventing the flow of electricity.

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Metals

Materials with very high conductivity, allowing easy flow of electricity.

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Junction Diode

A two-terminal electronic device that allows current to flow in only one direction.

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Bipolar Junction Transistor (BJT)

A three-terminal device that amplifies or switches electronic signals.

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Electrical Conductivity

The measure of how easily electricity flows through a material.

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Electronic Devices

Devices where the controlled flow of electrons is achieved, serving as the foundation of electronic circuits.

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Vacuum Tube

An early electronic device using vacuum to control electron flow, with varying numbers of electrodes (anode, cathode, grid).

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Cathode

The heated electrode in a vacuum tube that emits electrons.

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Anode

The electrode in a vacuum tube that collects electrons.

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Valves

These devices generally allow current to flow only in one direction.

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Advantages of Semiconductors

Semiconductors are small, consume less power, operate at lower voltages, and have a longer lifespan compared to vacuum tubes.

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Charge Carrier Control in Semiconductors

External factors like light, heat, or voltage can change the number of charge carriers in a semiconductor, controlling current flow.

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Internal Charge Flow in Semiconductors

The supply and flow of charge carriers in semiconductors happen within the solid material itself.

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Semiconductor Advantages over Vacuum Tubes

Vacuum tubes need a large evacuated space and external heating, while semiconductors do not.

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Energy Bands in Solids

The energy levels occupied by electrons in a solid form continuous bands rather than discrete levels seen in isolated atoms.

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Valence Band

The energy band containing the energy levels of valence electrons, which are usually bound to the atom.

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Conduction Band

The energy band above the valence band, typically empty. Electrons here can freely move and contribute to conductivity.

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Energy Band Gap

The energy difference between the valence band and the conduction band. If this gap is small, electrons can easily move to the conduction band, resulting in good conductivity; if large, the material is an insulator.

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Overlapping Energy Bands

The overlapping of the valence and conduction bands, resulting in easy electron movement between them, leading to good conductivity.

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Doping

The process of adding impurities to a semiconductor to modify its conductivity. This can be done by adding elements with more or fewer valence electrons than the semiconductor.

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Conduction in Semiconductors

In semiconductors, the movement of electrons is from the valence band to the conduction band due to thermal energy, allowing for a small but measurable flow of electricity.

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Covalent Bonding in Semiconductors

A covalent bond occurs when two neighboring atoms share a pair of electrons, holding them together in a crystal lattice.

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Energy Gap in Semiconductors

The energy required to excite an electron from the valence band to the conduction band in a semiconductor.

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Hole Formation in Semiconductors

When an electron breaks free from a bond in a semiconductor, it leaves a vacant spot with a positive charge, called a hole.

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Intrinsic Semiconductor Properties

The intrinsic semiconductor has an equal number of free electrons and holes, contributing to its conductivity.

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Energy Gap (Eg)

The energy gap determines how easily electrons can move to the conduction band and conduct electricity in a material.

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Valence Band (EV)

The energy band where electrons are tightly bound to the atoms and don't easily conduct electricity.

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Conduction Band (EC)

The energy band where electrons are free to move and conduct electricity.

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Excitation of Electrons

Electrons in the valence band can be excited to the conduction band using this energy.

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Depletion Layer

A region formed at the junction of p-type and n-type semiconductors, where charge carriers are depleted.

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Junction Potential Barrier

A potential difference across the p-n junction due to the depletion layer.

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Biasing a p-n Junction

Applying a voltage to a p-n junction to control the current flow.

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Study Notes

Semiconductor Electronics: Materials, Devices, and Simple Circuits

  • Devices control electron flow, fundamental to electronic circuits.
  • Older devices (valves) were vacuum tubes, bulky, high-power consumption, and low reliability.
  • Semiconductor devices are smaller, consume less power, operate at lower voltages, and have longer lifespans.
  • Semiconductors enable controlled flow of charge carriers via simple excitations (light, heat, voltage).
  • Materials are classified by their conductivity:
    • Metals: low resistivity (high conductivity).
    • Semiconductors: intermediate resistivity (conductivity).
    • Insulators: high resistivity (low conductivity).
  • Elemental semiconductors include silicon (Si) and germanium (Ge).
  • Compound semiconductors (like CdS, GaAs) are also used in devices.
  • Energy bands dictate electron behavior in solids.
  • Valence band holds valence electrons, while conduction band holds electrons free to move.
  • Energy gap (Eg) separates valence and conduction bands.
  • Insulators have a large Eg, impeding electron movement.
  • Metals have overlapping bands, enabling easy electron flow.
  • Semiconductors have a small Eg, allowing some electrons to move between bands at room temperature.
  • Intrinsic semiconductors have equal electron and hole concentrations.
  • Extrinsic semiconductors are doped (impurities added).
  • N-type semiconductors have extra electrons (donors).
  • P-type semiconductors have extra holes (acceptors).
  • P-n junctions are crucial for semiconductor devices like diodes.
  • P-n junctions create a depletion region with no free charge carriers.
  • Applied voltage (bias) affects junction behavior (forward or reverse).
  • Diodes allow current in one direction (rectifier).
  • Half-wave rectifiers only use current during half the input cycle.
  • Full-wave rectifiers use current during both input cycle halves.
  • Important concepts relate to different device types and characteristics.

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Semiconductor Electronics: Materials, Devices and Simple Circuits PDF

Description

Explore the fundamentals of semiconductor electronics, including the properties of various materials and devices. Understand the evolution from vacuum tubes to modern semiconductor devices, and learn about their role in controlling electron flow. This quiz covers essential concepts such as conductivity classification, energy bands, and key semiconductor materials.

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