Semiconductor Electronics Quiz

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Questions and Answers

What is an insulator?

An insulator is a material that has a very high resistance to the flow of electricity. This means that very little electric current can flow through an insulator. Examples of insulators include rubber, wood, glass, and air.

Which of the following is NOT a property of a semiconductor?

  • Conductivity increases with increasing temperature
  • Conductivity is intermediate to that of conductors and insulators
  • Conductivity is always high (correct)
  • Conductivity can be increased by adding impurities

In an intrinsic semiconductor, what is the relationship between the number of free electrons and the number of holes?

  • The number of free electrons is much less than the number of holes
  • The number of free electrons is not related to the number of holes
  • The number of free electrons is much greater than the number of holes
  • The number of free electrons is equal to the number of holes (correct)

What is doping?

<p>Doping is the process of intentionally adding impurities to a semiconductor material. This is done to control the semiconductor's electrical conductivity and to make it more useful for specific applications.</p> Signup and view all the answers

In an n-type semiconductor, which type of charge carrier is the majority carrier?

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

What is a p-n junction?

<p>A p-n junction is a boundary formed between a p-type semiconductor and an n-type semiconductor. It forms the basis for many semiconductor devices, like diodes and transistors.</p> Signup and view all the answers

What is the depletion region in a p-n junction?

<p>The depletion region is a thin layer that forms at the junction between a p-type semiconductor and an n-type semiconductor. It's created by the diffusion of charge carriers across the junction, and it is characterized by a lack of free charge carriers.</p> Signup and view all the answers

What is the barrier potential in a p-n junction?

<p>The barrier potential is a potential difference that builds up across the depletion region in a p-n junction. It is created by the fixed positive and negative charges within the depletion region.</p> Signup and view all the answers

What happens to the width of the depletion region in a p-n junction when it is forward biased?

<p>The width of the depletion region decreases (D)</p> Signup and view all the answers

What happens to the width of the depletion region in a p-n junction when it is reverse biased?

<p>The width of the depletion region increases (A)</p> Signup and view all the answers

What is a diode?

<p>A diode is a semiconductor device that allows current to flow easily in one direction (forward bias) but strongly resists current flow in the opposite direction (reverse bias).</p> Signup and view all the answers

What is the difference between a diode and a transistor?

<p>While both transistors and diodes are built from semiconductors, diodes are two-terminal devices that act as a gate for current flow, while transistors are three-terminal devices that can amplify or switch a signal.</p> Signup and view all the answers

What is rectification?

<p>Rectification is the process of converting alternating current (AC) into direct current (DC). This involves limiting the flow of current in one direction while allowing current to pass freely in the opposite direction.</p> Signup and view all the answers

What is a half-wave rectifier?

<p>A half-wave rectifier is a circuit that uses a diode to allow only one half-cycle of an AC waveform to pass through, resulting in a pulsating DC output.</p> Signup and view all the answers

What is the dynamic resistance of a diode?

<p>The dynamic resistance of a diode is a measure of its resistance to changes in current at a particular voltage point. It varies depending on the operating point of the diode.</p> Signup and view all the answers

The forward bias dynamic resistance of a diode is much lower than the reverse bias dynamic resistance.

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

How is an n-type semiconductor formed?

<p>An n-type semiconductor is made by adding a small amount of pentavalent dopant element, such as phosphorus or arsenic, to a pure semiconductor material like silicon or germanium.</p> Signup and view all the answers

Flashcards

Conductors

Materials with high conductivity (low resistivity), where the conduction band either overlaps with the valence band or is partially filled, enabling free electron movement.

Semiconductors

Materials with conductivity between conductors and insulators, with a small energy gap between the valence band and conduction band. At room temperature, some electrons can jump to the conduction band.

Insulators

Materials with very low conductivity (high resistivity), with a large energy gap between the valence band and conduction band. Electrons cannot easily jump to the conduction band.

Energy Band

The group of closely spaced energy levels that electrons in a solid can occupy.

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Valence Band

The energy band containing the valence electrons, which are responsible for chemical bonding.

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Conduction Band

The energy band containing conduction electrons, which are free to move and carry electrical current.

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Energy Gap (Eg)

The energy difference between the highest energy level in the valence band and the lowest energy level in the conduction band.

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Intrinsic Semiconductor

A pure semiconductor with poor conductivity at absolute zero temperature. Its conductivity increases with temperature.

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Doping

The process of adding impurities to an intrinsic semiconductor to increase its conductivity.

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n-type Semiconductor

A semiconductor with impurities that donate extra electrons to the conduction band, making it more conductive. The majority carriers are electrons.

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p-type Semiconductor

A semiconductor with impurities that accept electrons from the valence band, creating holes and increasing conductivity. The majority carriers are holes.

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p-n Junction

The interface between a p-type and an n-type semiconductor, where a depletion region forms due to diffusion and drift of charge carriers.

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Depletion Region

The region near the p-n junction where there are few free charge carriers due to diffusion and drift of majority charge carriers.

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Barrier Potential (V0)

The electric potential difference across the p-n junction due to the presence of fixed ions in the depletion region.

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Forward Current

The current that flows across the p-n junction when the diode is forward biased.

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Reverse Saturation Current

The current that flows across the p-n junction when the diode is reverse biased. It is very small and almost constant.

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Breakdown Voltage (Vbr)

The voltage across the diode at which the reverse current increases dramatically.

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Rectifier

The device that converts alternating current (AC) into direct current (DC).

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Half-Wave Rectifier

A rectifier circuit that uses a single diode to allow current to flow only during one half of the AC cycle.

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Full-Wave Rectifier

A rectifier circuit that uses two diodes to allow current to flow during both halves of the AC cycle, resulting in a DC output with ripple.

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Rectification

The process of converting an AC signal into a DC signal.

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Forward Resistance

The resistance of a diode when forward biased.

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Reverse Resistance

The resistance of a diode when reverse biased. It is much higher than forward resistance.

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Dynamic Resistance

The ratio of the change in voltage to the change in current in a diode.

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Threshold Voltage (Cut-In Voltage)

The voltage at which a diode begins to conduct significant forward current.

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Semiconductor Diode

A semiconductor device consisting of a p-n junction with metallic contacts for applying an external voltage.

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Tetravalent Element

An element with four valence electrons, used in semiconductors, commonly silicon (Si) and germanium (Ge).

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Pentavalent Element

An element with five valence electrons, used as a dopant to create n-type semiconductors. Examples include phosphorus (P) and arsenic (As).

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Trivalent Element

An element with three valence electrons, used as a dopant to create p-type semiconductors. Examples include boron (B) and aluminum (Al).

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Diffusion Current

The current due to the movement of majority charge carriers across the p-n junction, driven by the concentration gradient.

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Drift Current

The current due to the movement of minority charge carriers across the p-n junction, driven by the electric field.

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Doping Process

The process by which a semiconductor becomes an n-type or p-type semiconductor due to the addition of impurities.

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Study Notes

Semiconductor Electronics: Materials, Devices and Simple Circuits

  • Learning Objectives: After studying this unit, learners will understand the classification of solids based on conductivity, energy band theory, intrinsic and extrinsic semiconductors, p-n junction diodes, and their characteristics.

Introduction

  • Vacuum Tubes vs. Semiconductor Devices: Semiconductor devices replaced vacuum tubes because they are less bulky, consume less power, and are more reliable.

Classification of Solids

  • Conductors: Solids with high conductivity (low resistivity). Conductivity ranges from 10² to 10⁸ S m⁻¹. Examples include aluminum, copper, silver, and gold.
  • Insulators: Solids with low conductivity (high resistivity). Conductivity ranges from 10⁻¹¹ to 10⁻¹⁹ S m⁻¹. Examples include rubber, plastic, mica, and glass.
  • Semiconductors: Solids with conductivity intermediate to metals and insulators. Conductivity ranges from 10⁻¹ to 10⁶ S m⁻¹ and resistivity ranges from 10⁵ to 10⁹ Ωm. Examples include silicon and germanium.

Band Theory of Solids

  • Energy Bands: Closely spaced energy levels in solids form energy bands.
  • Valence Band: Energy levels occupied by valence electrons.
  • Conduction Band: Energy levels above the valence band, occupied by conduction electrons.
  • Energy Gap (Eg): The separation in energy between the valence and conduction bands. A larger energy gap implies an insulator, a smaller energy gap a semiconductor, a gap of zero implies a conductor.

Intrinsic Semiconductor

  • Definition: A pure semiconductor with no impurities. Its conductivity is low at absolute zero temperature, but increases progressively with increasing temperature.
  • Electron-Hole Pair Generation: Thermal energy enables electrons to jump from the valence band to the conduction band, creating electron-hole pairs (free electrons and holes).

Extrinsic Semiconductor

  • Definition: An impure semiconductor with added impurities to increase conductivity.
  • Doping: The process of adding impurities to an intrinsic semiconductor.
  • N-type Semiconductor: Pentavalent impurities (e.g., phosphorus, arsenic, antimony) are added. The extra valence electrons from the impurity atoms become conduction electrons. Electrons are majority carriers.
  • P-type Semiconductor: Trivalent impurities (e.g., boron, aluminum, gallium) are added. The missing valence electrons create 'holes' that behave as positive charge carriers. Holes are majority carriers.

p-n Junction Diode

  • Formation: A p-n junction is formed when a p-type and an n-type semiconductor are joined together.
  • Depletion Region: A region near the junction where majority charge carriers are depleted, creating an electric field that opposes further diffusion of charge carriers.
  • Forward Bias: Applying positive voltage to the p-side and negative voltage to the n-side reduces the barrier potential, allowing current flow.
  • Reverse Bias: Applying negative voltage to the p-side and positive voltage to the n-side increases the barrier potential, decreasing current flow.
  • Characteristics: The I-V (current-voltage) characteristics of a diode exhibit different behaviors under forward and reverse bias.

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