- A semiconductor is a substance that has properties between an insulator and a conductor. The semiconductor materials are mainly used for manufacturing electronic devices like transistor, diode and the integrated circuits. So whenever the voltage is applied to this semiconductor, then allows the moderate amount of current and moreover that by adding the impurities, the conductivity of the semiconductor material can be changed. This property is very useful for designing the various electronic devices.
- If there is a gap between the valence and the conduction bands however it is small enough so that the valence electrons can reach the conduction band when the energy is provided by an applied voltage. So silicon, germanium and the gallium arsenide are the few examples of the semiconductor material. So here the most widely used semiconductor material is the silicon hence the name Silicon Valley in California.
- Now, the atomic number of the silicon is 14. So if we see the atomic structure of this silicon, it has 14 protons and the 14 electrons. So these 14c protons reside in the nucleus and 14 electrons rotate around this nucleus. And if you see the outermost orbit of the silicon, then it has 4 electrons.
Silicon atom has 4 valence electrons, so each silicon atom combine to form a solid, and then they arrange themselves in a particular pattern which is known as the crystal. And in this crystal structure each silicon atom shares its four electron with the neighboring atoms and the sharing of the electron happens in such a way that, each silicon atom has 8 valence electrons. And in this way, by sharing the electrons these silicon atoms forms the covalent bond. - Now, at the temperature just above the 0-degree Kelvin, due to the thermal energy, the atoms in the silicon crystal starts vibrating. And due to this vibration, some electrons may get enough energy, so that they can break these covalent bonds. And by breaking these bonds, this electron will act as a free electron. So at room temperature you will find many such free electrons in this silicon structure.
- Now whenever this electron, departs from its position then it creates a vacancy at that particular position. And this vacancy is known as the hole. Now, we know that the charge of the electron is 1.6 x 10-19C, and it has a negative charge. So by not having an electron at a particular position creates a positive charge and this positive charge is known as the hole. So this hole can attract the other free electrons which are roaming in this vicinity. For any silicon structure, at room temperature, the generation and the recombination of holes and electrons happens continuously. For generated electron, the hole is also getting generated. So we can say that at the given temperature the equal number of holes and electrons are created in this silicon structure. As the electrons are moving from one place to the other place, the holes are also moving from one place to the other place.
