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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 the energy required for electrons to transition from the valence band to the conduction band. Insulators have a large band gap making it difficult for electrons to achieve this transition, hence preventing the flow of current. Semiconductors possess a smaller band gap that allows for some electrons to make the transition and permit the flow of current.

Step by step solution

01

Understand The Band Theory

The Band Theory is a model that explains the properties of solid materials in terms of energy bands. Energy bands consists of a large number of closely spaced energy levels that electrons can occupy. The two relevant bands for this exercise are the Valence Band, which contains the outer shell electrons that are involved in bonding of the atom, and the Conduction Band, which is the band of electron orbitals that electrons can jump up to from the valence band.
02

Understand The Band Gap

The Band Gap is the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from the valence band to the conduction band if they are provided with sufficient energy. The size of the band gap determines how much energy is needed for this jump.
03

Differentiating Insulator and Semiconductor

Materials with a large band gap, typically greater than 3 electron-volts, are Insulators. In these materials, the energy required to push an electron from the valence to the conduction band (the band gap) is so high that there are very few electrons that can gain this much energy, thus very little to no current can flow. On the other hand, materials with smaller band gaps, typically less than 3 electron-volts, are referred as Semiconductors. The energy required to move an electron from the valence to the conduction band is sufficiently small to allow some electrons to make this transition thus current can flow in the material.

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