Question

Use the band model to describe differences among insulators, conductors, and semi-conductors. Also use the band model to explain why each of the following increases the conductivity of a semi-conductor.

a. increasing the temperature

b. irradiating with light

c. adding an impurity

How do conductors and semi-conductors differ as to the

effect of temperature on electrical conductivity?

Short answer

1. As temperature increases, more electrons jump into the conduction band
2. It gains sufficient energy to jump into the conduction band
3. Creating an easier path for electrons to jump from filled to unfilled energy levels.

Step-by-step solution

Given Information

The band model can be used to describe differences among insulators, conductors, and semi-conductors.

Conductors, Insulators, and Semi-conductors

Conductor: The energy difference between filled and unfilled molecular orbitals is minimum. Due to the minimum band energy gap, electrons can easily move into the conduction band.

Semi-conductor: The energy difference between filled and unfilled molecular orbitals is smaller than in insulators. So some electrons can jump into conduction bands. So semi-conductors have intermediate conductivity.

Insulator: The energy difference between filled and unfilled molecular orbital is large. So electrons cannot move from the filled orbital to the conduction band.

Semi-conductors

As the temperature increases, more electrons in the filled molecular have sufficient kinetic energy to jump into the conduction band.

1. A photon of light is absorbed by an electron that then has sufficient energy to jump into conduction bands.
2. An impurity adds electron energy near that of conduction bands or creates holes at energies in the previously filled molecular orbital.
3. Both n-type and p-type semi-conductors increase the conductivity by creating an easier path for electrons to jump from the filled to the conduction band.