Semiconductor Diodes and p-n Junctions

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Questions and Answers

What phenomenon occurs at the atomic level in any slab in contact with flowing charge carriers?

Discontinuity in charge flow (correct)

Localized electric fields

Negligible roughness

Continuous atomic contact

Which statement best describes the configuration of a semiconductor diode?

It has three terminals, two of which are connected to an external voltage

It operates solely on intrinsic semiconductor materials

It consists of two p-type semiconductors bonded together

It is a two terminal device with a p-n junction (correct)

In the context of a p-n junction diode under forward bias, where does most of the voltage drop occur?

Across both sides equally

In the metallic contacts

Across the depletion region (correct)

In the external circuit

What does the direction of the arrow in a p-n junction diode symbolize?

Conventional current flow under forward bias Signup and view all the answers

What happens to the equilibrium barrier potential of a p-n junction diode when an external voltage is applied?

It decreases, allowing current to flow Signup and view all the answers

What is the primary role of the dopant in extrinsic semiconductors?

To reduce the intrinsic concentration of minority carriers. Signup and view all the answers

In an n-type Si semiconductor, where is the donor energy level (ED) located?

Slightly below the bottom EC of the conduction band. Signup and view all the answers

What happens to the majority carriers when thermal minority carriers meet them?

Majority carriers are destroyed. Signup and view all the answers

What primarily dominates the density of holes in the valence band of a p-type semiconductor at room temperature?

Ionization of acceptor atoms. Signup and view all the answers

What occurs when an electron from the valence band jumps to the acceptor energy level (EA) in a p-type semiconductor?

It ionizes the acceptor negatively and leaves a hole. Signup and view all the answers

Why do majority carriers help in reducing the intrinsic concentration of minority carriers?

They increase the chances of destruction of minority carriers. Signup and view all the answers

How are the conduction electrons in an n-type semiconductor primarily generated?

From donors ionizing at room temperature. Signup and view all the answers

What happens to holes in a p-type semiconductor at room temperature?

They are predominantly due to ionization of acceptor atoms. Signup and view all the answers

What happens to electrons in the valence band when they gain external energy?

They move into the conduction band, creating vacant levels. Signup and view all the answers

At absolute zero, what characterizes the conduction band in Si and Ge?

It is completely empty of electrons. Signup and view all the answers

What is the maximum number of electrons that can occupy the outermost orbit of Si and Ge?

8N Signup and view all the answers

What is the energy gap between the valence band and conduction band known as?

Energy band gap Signup and view all the answers

In the context of the discussed materials, what does the term 'valence electrons' refer to?

Electrons that are involved in bonding. Signup and view all the answers

Which of the following statements is true about the outer orbit electrons for Si and Ge?

Both Si and Ge have 4 electrons in their outermost orbit. Signup and view all the answers

Which statement best describes the valence band at absolute zero temperature?

It is completely filled with electrons. Signup and view all the answers

What effect does the distance between atoms have on the energy states in a crystal?

It influences the grouping of energy levels into bands. Signup and view all the answers

What is the relationship between the current produced by electrons and holes in a semiconductor?

The total current is the sum of the currents from both electrons and holes. Signup and view all the answers

At what temperature does an intrinsic semiconductor behave like an insulator?

At absolute zero, 0 K. Signup and view all the answers

What induces the excitation of electrons from the valence band to the conduction band in intrinsic semiconductors?

Thermal energy at temperatures greater than 0 K. Signup and view all the answers

What happens at equilibrium in a semiconductor?

The rates of generation and recombination of charge carriers are equal. Signup and view all the answers

Which of the following statements is true about recombination in semiconductors?

Recombination occurs when an electron collides with a hole. Signup and view all the answers

What is the significance of thermally excited electrons in an intrinsic semiconductor at T > 0 K?

They partially occupy the conduction band. Signup and view all the answers

Why does carbon behave as an insulator while silicon and germanium behave as intrinsic semiconductors?

Carbon has no free electrons while silicon and germanium have more available electrons. Signup and view all the answers

What does the energy-band diagram of an intrinsic semiconductor show at T > 0 K?

It shows thermally generated electron-hole pairs. Signup and view all the answers

What is the energy gap (Eg) for insulators?

Eg > 3 eV Signup and view all the answers

How does a p-n junction behave in forward bias?

The junction barrier decreases. Signup and view all the answers

What happens to electrons during conduction in a semiconductor?

They can be excited from the valence band. Signup and view all the answers

What forms the depletion layer in a p-n junction?

Immobilized ion-cores Signup and view all the answers

In a semiconductor with low resistivity, how would the energy gap (Eg) be characterized?

Eg < 0.2 eV Signup and view all the answers

What is a primary use of diodes in electronic circuits?

Rectifying AC voltage Signup and view all the answers

How can the type of semiconductor be changed in compound semiconductors?

By altering the relative stoichiometric ratio Signup and view all the answers

What is the primary effect of applying a reverse bias to a p-n junction?

Increase in barrier height Signup and view all the answers

What is the typical resistivity range for metals?

10–2 to 10–8 W m Signup and view all the answers

What defines an intrinsic semiconductor?

Has an equal number of electrons and holes Signup and view all the answers

In n-type semiconductors, what is the relationship between electrons and holes?

ne >> nh Signup and view all the answers

Which type of atom is used to create n-type semiconductors?

Pentavalent atoms Signup and view all the answers

What characterizes holes in semiconductors?

They are vacancies for electrons with an effective positive charge Signup and view all the answers

Which statement is true regarding the conduction band?

Electrons in this band are free to move and contribute to conductivity Signup and view all the answers

What is a characteristic of p-type semiconductors?

nh >> ne Signup and view all the answers

Charge neutrality in a semiconductor is maintained by which of the following relationships?

nenh = ni2 Signup and view all the answers

Study Notes

Semiconductor Electronics: Materials, Devices, and Simple Circuits

Devices control electron flow, forming electronic circuits.
Vacuum tubes (valves), like diodes, triodes, tetrodes, and pentodes, were predecessors to transistors.
Vacuum tubes are bulky, high-voltage, and less reliable.
Semiconductors offer controlled charge carrier flow at low voltage and power.
Simple stimuli (light, heat, voltage) alter semiconductor charge carrier count.

Classification of Materials

Metals: Low resistivity, high conductivity (σ ~ 10² – 10⁸ Ω⁻¹m⁻¹).
Semiconductors: Intermediate resistivity, intermediate conductivity (σ ~ 10⁵ – 10⁶ Ω⁻¹m⁻¹).
Insulators: High resistivity, low conductivity (σ ~ 10⁻¹¹ – 10⁻¹⁹ Ω⁻¹m⁻¹).
Resistivity values are indicative, not sole classification criteria.

Elemental Semiconductors

Silicon (Si) and Germanium (Ge) are commonly used.
These form covalent bonds in a crystal structure.

Intrinsic Semiconductors

A pure semiconductor material.
Charge carriers (electrons and holes) are generated due to thermal excitation.
Number of electrons equals the number of holes (nₑ = n = nᵢ).

Extrinsic Semiconductors

Doping pure semiconductors with impurities to improve conductivity.
n-type: Pentavalent dopants add extra electrons (e.g., Arsenic, Antimony).
p-type: Trivalent dopants create electron vacancies (holes) (e.g., Indium, Boron).

p-n Junction

p-type and n-type semiconductors joined.
Forward bias: Applied voltage opposes depletion region; large current.
Reverse bias: Applied voltage enhances depletion region; very little current.

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Description

Test your understanding of semiconductor diodes, particularly focusing on p-n junctions and their behavior under various biases. This quiz covers key phenomena, voltage drops, and configurations related to diodes. Perfect for students of electronics or anyone interested in semiconductor technology.