Electron Structure in Isolated Atoms vs. Solids

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Questions and Answers

What is the primary difference between the electron structure of an isolated atom and a solid material?

Energy levels in isolated atoms are continuous, while in solids they are discrete.

Isolated atoms have a valence band and a conduction band, while solids do not.

Isolated atoms have discrete energy levels, while solids have continuous energy bands. (correct)

Solids have a band gap, while isolated atoms do not.

What happens to the electron in the donor energy level during electron excitation involving a donor impurity atom?

It moves from the donor energy level to the conduction band, releasing an additional free electron. (correct)

It moves from the conduction band to the valence band, creating a hole.

It moves from the valence band to the conduction band, creating a hole.

It remains in the donor energy level, doing nothing.

Why do holes not form when electrons are excited from a donor impurity atom?

Because the electrons come from the valence band.

Because the electrons come from the conduction band.

Because the electrons come from an energy level below the conduction band. (correct)

Because the donor atom is ionized.

What determines the electrical properties of a solid material?

The size of the band gap. Signup and view all the answers

What is the result of the periodic potential of the crystal lattice in solids?

The formation of continuous energy bands. Signup and view all the answers

In a p–n junction, what happens to electrons and holes under forward bias?

Electrons move from the n-side to the p-side, while holes move from the p-side to the n-side. Signup and view all the answers

What is the primary difference in electron motion between forward and reverse bias in a p–n junction?

Electrons move in opposite directions under forward and reverse bias. Signup and view all the answers

What is the result of ionizing a donor atom in a semiconductor material?

A free electron is released into the conduction band. Signup and view all the answers

What happens to the potential barrier in a p–n junction under forward bias?

It is reduced, allowing current flow. Signup and view all the answers

What is the primary reason for minimal current flow in a p–n junction under reverse bias?

The potential barrier is increased, preventing majority carriers from crossing the junction. Signup and view all the answers

What is the characteristic of semiconductors that allows them to control conductivity?

Smaller band gap, allowing some electron excitation at room temperature. Signup and view all the answers

What is the primary difference between metals and semimetals?

Semimetals have fewer charge carriers than metals. Signup and view all the answers

What is the primary reason for electron flow in metals?

The conduction band and valence band overlap. Signup and view all the answers

What is the primary characteristic of insulators?

Large band gap between valence and conduction bands. Signup and view all the answers

What is the result of electron excitation in semiconductors?

Electrons are excited to the conduction band, allowing moderate conductivity. Signup and view all the answers

What is the primary difference between intrinsic and extrinsic semiconductors?

Intrinsic semiconductors are pure, while extrinsic semiconductors are doped. Signup and view all the answers

Study Notes

Electron Structure of Isolated Atoms vs. Solid Materials

Electron structure of an isolated atom consists of discrete energy levels with electrons occupying specific orbitals defined by quantum numbers
Electron structure of a solid material features continuous energy bands formed by the overlap of atomic orbitals due to close packing of atoms
This interaction creates a valence band and a conduction band, separated by a band gap, determining the material's electrical properties (insulator, semiconductor, or conductor)

Electron Excitation Involving Donor Impurity Atom

No hole is generated when an electron is excited from a donor energy level to the conduction band
This is because the donor energy level lies just below the conduction band, and the excitation process releases a free electron into the conduction band without creating an electron vacancy in the valence band

Electron and Hole Motions in a p-n Junction

Under forward bias, the potential barrier is reduced, allowing electrons from the n-side to move into the p-side and holes from the p-side to move into the n-side, resulting in significant current flow
Under reverse bias, the potential barrier is increased, preventing majority carriers from crossing the junction, resulting in minimal current flow
Minority carriers (electrons on the p-side and holes on the n-side) are pulled toward the junction, but their contribution to current is negligible

Electron Band Structures for Solid Materials

Solid materials exhibit four possible electron band structures: metals, insulators, semiconductors, and semimetals
Metals: conduction band and valence band overlap, allowing electrons to flow freely and making them good conductors of electricity
Insulators: large band gap between valence band and conduction band, preventing electron flow at room temperature and thus inhibiting conductivity
Semiconductors: smaller band gap, allowing some electron excitation at room temperature, enabling moderate conductivity that can be controlled by doping
Semimetals: overlapping conduction and valence bands similar to metals but with fewer charge carriers, resulting in unique electrical properties that vary with temperature and doping

Electron Excitation Events

Metals: electron excitation is unnecessary, as electrons can flow freely between conduction and valence bands
Semiconductors (intrinsic): thermal energy can excite electrons from the valence band to the conduction band, creating free electrons and holes
Semiconductors (extrinsic): doping with donor or acceptor impurities enables controlled excitation of electrons and creation of free electrons and holes
Insulators: high-energy radiation or thermal energy can excite electrons from the valence band to the conduction band, creating free electrons and holes, but this is rare at room temperature

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Description

Learn about the differences in electron structure between isolated atoms and solid materials, including discrete energy levels and continuous energy bands.