When voltage is applied to semiconductor devices, electron current flows toward the positive side of the source and holes current flows towards the negative side of the source. Such a situation occurs only in a semiconductor material.

Silicon and Germanium are the most common semiconductor materials. Generally, the conductivity of a semiconductor lies in between the conductivities of metals and insulators.

Germanium as a Semiconductor

Following are some important points about Germanium −

• There are four electrons in the outermost orbit of germanium. In bonds, atoms are shown with their outer electrons only.

• The germanium atoms will share valence electrons in a covalent bond. This is shown in the following figure. Germanium are the ones that are associated with the covalent bonding. The crystalline form of germanium is called the crystal lattices. This type of structure has the atoms arranged in the way as shown in the following figure.

• In such an arrangement, the electrons are in a very stable state and thus are less appropriate to be associated with conductors. In the pure form, germanium is an insulating material and is called as an intrinsic semiconductor.

The following figure shows the atomic structures of Silicon and Germanium.

Silicon as a Semiconductor

Semiconductor devices also use silicon in the manufacturing of various electronic components. The atomic structure of silicon and germanium is shown in the above figure. The crystal lattice structure of silicon is similar to that of Germanium.

Following are some of the important points about Silicon −

• It has four electrons in its outermost shell like germanium.

• In pure form, it is of no use as a semiconductor device.

• A desired amount of conductivity can be obtained by adding up of impurities.

• Adding up of impurity must be done carefully and in a controlled environment.

• Depending on the type of impurity added, it will create either an excess or a deficit of electrons.

The following figure shows the intrinsic crystal of Silicon.