You must first study the semiconductor, a substance that is neither an insulator nor a conductor, in order to comprehend how diodes, transistors, or any integrated circuit function. Let's first examine what distinguishes a substance as a conductor or an insulator before learning about semiconductors.
What is a conductor?
Copper is a good conductor, as is common knowledge. When we examine its atomic structure, the cause becomes clear.
A copper atom's nucleus contains 29 protons (positive charge). There are 29 negatively charged electrons revolving around the nucleus. Two electrons are in the first orbit, eight are in the second, eighteen are in the third, and one is in the outer orbit.
The outer orbit, which determines the conductivity of the atom, is all that matters in electronics. Valence orbit is another name for it.
Net Charge
We define the core of an atom as the nucleus and all of the inner orbitals in order to determine the net charge of an atom.
A copper atom's nucleus (+29 protons) and first three orbits make up its core (-28 electrons). Because of this, a copper atom's nucleus has a net charge of +1 (plus 29 protons and minus 28 electrons).
An illustration of a copper atom's core and valence orbit is shown in the following figure.
Free Electrons
The core and valence electron only have a very weak attraction since the core has a net charge of only 1. This electron is easily freed from a copper atom by even a nominal voltage, which then allows it to go through the substance. Due to this, the valence electron is frequently referred to as a free electron. And the movement of these unbound electrons is known as current.
Like other metals, copper has a lot of free electrons, which is what makes it an excellent conductor of electricity.
What is Insulators
One of the best insulators is neon. Let's examine its atomic composition. Ten protons and ten electrons make up an atom of neon. Two electrons are in the first orbit, and the other eight are in the valence orbit. The 10 protons in the nucleus and 2 electrons in the first orbit give the core of a neon atom a net charge of +8. The core diagram of an atom of neon is shown in the following figure. Because the core has a net charge of +8, the inward pull felt by the valence electrons is very large. Insulators therefore don't conduct because there aren't any free electrons present.
Note
The valence electrons in insulators are literally ripped away from their atoms when a high enough voltage is applied to the material. Conduction will result from this. It will seem like an arc or flash in the air. The heat produced will cause solid items to char.
What is Semiconductors
A substance that is neither a good conductor nor an effective insulator is known as a semiconductor. The best semiconductors, as one might anticipate, have four valence electrons.
A semiconductor is anything like silicon. Let's examine its atomic composition.
14 protons and 14 electrons make up an atom of silicon. Two electrons are present in the first orbit, while eight electrons are present in the second orbit. The valence orbit is home to the four remaining electrons.
Because there are 10 electrons in the first two orbits and 14 protons in the nucleus, the core of a silicon atom has a net charge of +4. The silicon atom's core diagram is shown in the following figure.
The quantity of valence electrons affects an atom's conductivity. The best conductor is an atom with just one valence electron. An atom is at its finest as an insulator when it has eight valence electrons.
As you can see, a silicon atom contains four valence electrons, which causes it to have intermediate electrical conductivity between insulators and conductors. Because of this, silicon is a semiconductor.
