Semiconductor device tutorial
Everything that has weight matters. According to the theory of the atom, all matter, whether solid, liquid or gas, is made up of atoms. An atom contains a central part called the nucleus, which contains neutrons and protons. Normally, protons are positively charged particles and neutrons are neutrally charged particles. Electrons which are negatively charged particles are arranged in orbit around the nucleus in a manner similar to the network of planets around the Sun. The following figure shows the composition of an atom.
Atoms of different elements have different numbers of protons, neutrons and electrons. To distinguish one atom from another or to classify different atoms, a number which indicates the number of protons in the nucleus of a given atom, is assigned to the atoms of each identified element. This number is called the element's atomic number . Atomiq numbersues of some of the elements associated with the study of semiconductors are given in the following table.
| Element || Symbol || Atomic number |
| Silicium || Si || 14 |
| Germanium || Ge || 32 |
| Arsenic || As || 33 |
| Antimony || Sb || 51 |
| Indium || In || 49 |
| Gallium || Ga || 31 |
| Bore || B || 5 |
Normally an atom has an equal number of protons and planetary electrons to keep its net charge at zero. Atoms frequently combine to form molecules or compounds stabilized by their available valence electrons.
The pro La combinaison free valence electrons is generally called a bond . Here are the different types of bonds that take place in combinations of atoms.
- Ionic bond
- Covalent bond
- Metallic bond
Now let's talk in detail of these atomic bonds.
Each atom seeks stability when atoms bind together to form molecules. When the valence band contains 8 electrons, it is said to be a stabilized condition . When the valence electrons of one atom combine with those of another atom to become stable, this is called an ionic bond .
If an atom has more than 4 valence electrons in the outer shell, it is looking for additional electrons. Such an atom is often called an acceptor .
If an atom contains less than 4 valence electrons in the shell external, they try to get out of these electrons. These atoms are known as donors .
In ionic bonds, donor and acceptor atoms frequently combine and the combination stabilizes. . Common salt is a common example of an ionic bond.
The following figures show an example of independent atoms and ionic bond.
We can see in the figure above that the sodium atom (Na) donates its 1 valence electron to the chloride atom (Cl) which has 7 valence electrons. The chloride atom immediately becomes negatively overbalanced when it gets the extra electron, which causes the atom to become a negative ion. While on the other hand, the sodium atom loses its valence electron and the sodium atom then becomes a positive ion.As we know, unlike charges attract, sodium and chloride atoms are bound together by an electrostatic force.
When the valence electronsneighboring atoms are shared with other atoms, a covalent bond takes place. In the covalent bond, ions do not form. This is a unique dissimilarity in covalent bond and ionic bond.
When an atom contains four valence electrons in the outer shell, it can share one electron with four neighboring atoms. A covalent force is established between the two bond electrons. These electrons alternately shift orbits between atoms. This covalent force binds individual atoms together. An illustration of the covalent bond is shown in the following figures.
In this arrangement, only the nucleus and valence electrons of each atom are displayed. Pairs of electrons are created because the individual atoms are linked together. In this case, five Atoms are needed to complete the bonding action. The bonding process is expanding in all directions. Each atom is now bonded together in alattice network and a crystal structure is formed by this lattice network.
The third type of bond usually occurs in good electrical conductors and is called l bond. In the l bond, an electrostatic force exists between the positive ions and the electrons. For example, the valence band of copper has an electron in its outer shell. This electron tends to move around the material between different atoms.
When this electron leaves an atom, it instantly enters the orbit of another atom. The process is repeated continuously. An atom becomes a positive ion when 'leaves an electron. It 's is ' s random process . This means that an electron is always linked to an atom. This does not mean that 's electron is associated with a particular orbit. It always moves in different orbits. Consequently, all atomsare likely to share all valence electrons.
Electrons hang around in a cloud that covers positive ions. This hovering cloud randomly binds electrons to ions. The following figure shows an example of copper l bonding .