As we know all materials are made with atoms. According to Bohr’s atomic model “An atom is a small element of a material that retains the properties of that material. These atoms are also responsible for electrical properties of a material. Bohr found there are tiny particles in an atom called Electrons which revolve around the center named Nucleus. The nucleus has positively charged particles called protons and neutral particles called Neutrons. The electron has negative charge.
How does current flow in electronics materials? The most important thing is to understand insights of an atom. Then we will be able to distinguish between them.
Conduction Basics in Electronic Materials
The electrons in an atom revolve around the nucleus in orbits. Some electrons are near the nucleus and some are away from the nucleus revolving in their respective orbits as shown in fig-1 below
You can see the nucleus (Blue Color) is surrounded by the orbits. The inner orbits and nucleus are parts of the core.
Valence Shell Definition
The outer most orbit is called “Valence Shell” and the electrons in the valence shell are called “valence electrons”.
The nucleus attract the electrons. The electrons near the nucleus are tightly bounded. The electrons in the valence shell are most loosely bounded because they are farthest as compared to electrons in the core. These valence electrons contribute in conduction. When these valence electrons absorb enough energy from external source they leave the valence shell and starts conducting.
The electrons which leave the valence shell and jumps into the space between atoms are called “free electrons”.
Types of Electronics Materials
The materials used in electronics are divided into three categories
1. What is Conductor?
A conductor is a material which has the ability of pass the electric current. The valence electrons are loosely bounded and can be freed easily. Its mean conductive materials have free electrons within the atoms as shown in fig-2. Examples are copper is a good conductor of electricity. Other conductor examples are Ferris, Silver etc.
Fig-2: A Conductive Material
2. What is Insulator?
In electronics insulator meaning a material tot able to pass electricity. An insulator material has very few free electrons between atoms. The valence electrons are tightly bounded with nucleus. Insulating materials do not allow current to flow through them. Their resistance is very high. Examples of insulator materials are plastic, glass, rubber etc.
3. What is Semiconductor?
A pure semiconductor material has conductivity between conductors and insulators. In other words this material is not a good conductor not a good insulator too. Semiconductor examples are silicon, gallium, germanium, antimony etc. They are also present in compound form, compound semiconductors are gallium arsenide, gallium nitrite and silicon carbide.
Band Gap Theory
According to Bohr’s atomic model, each orbit represents a band of energy. And when we move away from the nucleus the energy increases. Its mean the electrons near the nucleus have less energy while the electrons in the valence band have more energy.
Conduction Band and Valence Band
The energy band of the valence shell of an atom is the “valence band”. Whereas the valence electrons jumps into the space between atoms after absorbing energy. Now the electrons are in the “conduction band”.
What is Band Gap?
The difference between the energies of valence band and conduction band is called “Energy gap or band gap”.
An electron can’t jump from valence band to conduction band unless it must get the energy equal to band gap as shown in Fig-3
The band gap diagram of three types of electronics materials is given below in Fig-4
You can see above, in (c) the conduction band and valence band are overlapping in conductor materials. Its mean valence electrons need very little energy to move from valence band to conduction band. The semiconductor band gap is higher than conductors. The insulator band gap is highest, so electrons need very high energy to move to conduction band.