Question

In a silicon lattice, where should you look if you want to find (a) a conduction electron, (b) a valence electron, and (c) an electron associated with the 2psubshell of the isolated silicon atom?

Short answer

1. The conduction electron in a silicon lattice is found in the conduction band.
2. The valence electron in a silicon lattice is found in the outermost occupied shells of the atoms which is at the top of the valence band.
3. The electron associated with the 2p subshell is found above the Fermi level and below the bottom of the conduction band.

Step-by-step solution

The given data

A silicon lattice is given.

Understanding the concept of band structure

Usually, the free electrons responsible for the conduction are called the conduction electrons that flow from the top of the valence band to the bottom of the conduction band. Generally, the electrons present in the valence band, absorb energy from the environment and jump to the conduction band. Now, using the band structure concept, we can get that the 2p-orbital of the silicon lattice structure is a closely packed shell with a location above the Fermi level and below the conduction band. Fermi level is at the middle of both the bands for undoped silicon.

a) Calculation of the location of conduction electron

As per the concept, the conduction electrons which are responsible for the conduction of electricity are present in the conduction band.

b) Calculation of the location of valence electron

the energy band present just below the conduction band is known as a valence band.

The electrons present in the highest occupied level of the band are called valence electrons.

c) Calculation of the location of the 2p electron  

Using the concept of the band structure of the silicon lattice, we can see that the band structure is composed of closely packed lines. This also shows that the 2p-orbital of the silicon atom is located between the valence band and the conduction band that is more close to the conduction band.

Hence, the electrons present in 2p-orbital is found between the Fermi level and the bottom of the conduction band.