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Chapter 37: Problem 11

Why does the size of the band gap determine whether a material is an insulator or a semiconductor?

Short Answer

Expert verified
The size of the band gap determines whether a material is an insulator or a semiconductor because it influences how easily electrons can transition from the valence band to the conduction band. A large band gap, typical for insulators, makes this transition difficult, impeding electrical conductivity. Conversely, a small band gap, typical for semiconductors, makes this transition easier, allowing for electrical conductivity.

Step by step solution

01

Discuss the concept of band gap

The band gap is a key concept in solid-state physics, especially in semiconductors. It refers to the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. In these materials, electrons are forbidden to possess energy in the band gap.
02

Explain electrical conductivity

Electrical conductivity in materials is determined by the ease with which electrons can move from the valence band (where they are normally located) to the conduction band (where they can move freely, and thus conduct electricity). The ability of an electron to do this is determined by the size of the band gap.
03

Discuss how band gap size determines if a material is an insulator or a semiconductor

In insulators, the band gap is large. Seeking to acquire enough energy to overcome this gap, and transition from the valence band to the conduction band, is difficult for electrons, making insulators poor conductors of electricity. Conversely, in semiconductors, the band gap is small enough such that thermal energy is often sufficient to cause the electrons to move from the valence band to the conduction band, making semiconductors good conductors of electricity.

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