Demonstrative Video
Materials used in Electronics
Materials in terms of electrical properties can be grouped as:
Conductors
Semi-conductors
Insulators
Atoms combine to form solid crystalline material in a symmetrical pattern
Atoms are held together by covalent bonds, which are created due to valence electrons
4 valence electrons and 2e in inner shell
6 protons + 6 neutrons
Insulators
does not conduct electrical current under normal conditions
are compounds rather than single-element materials
have very high resistivities
Valence electrons are tightly bound to the atoms
rubber, plastics, glass, mica, and quartz
Conductors
easily conducts electrical current
most metals are good conductors
copper (Cu), silver (Ag), gold (Au), and aluminum (Al),
Only one valence electron very loosely bound to the atom
Semi-conductors
between conductors and insulators conduct electrical current
pure (intrinsic) state is neither a good conductor nor a good insulator
antimony (Sb), arsenic (As), astatine (At), boron (B), polonium (Po), tellurium (Te), silicon (Si), and germanium (Ge).
Compounds such as gallium arsenide, indium phosphide, gallium nitride, silicon carbide, and silicon germanium commonly used.
Single-element are characterized by four valence electrons.
Silicon is the most commonly
Band Gap
Free electrons after leaving the valence band exist in the conduction band
Energy gap or band gap : Energy difference between the bands
In conduction band electrons are free to move throughout the material and not tied to a atom
For insulators, the gap can be crossed only when breakdown conditions occur—as when a very HV is applied across the material
band gap depends on the semiconductor material
Semiconductor Atom Vs Conductor Atom
core includes everything except the valence electrons
Cu atom valence electron feels an attractive force of +1 compared to a that of silicon atom which feels an attractive force of +4
More force trying to hold a valence electron to the atom in silicon than in copper
Cu 4th shell (greater distance) than Si in 3rd shell
Electron farthest \(\rightarrow\) more energy \(\rightarrow\) loosely bound
Easier for Cu valence electron to escape than that of Si
Silicon and Germanium
Si used in diodes, transistors, integrated circuits, and other semiconductor devices.
Both Si and Ge have 4 valence electrons.
Valence electrons Ge in 4th shell while Si in 3rd shell, closer to the nucleus.
Ge valence electrons are at higher energy levels than those in Si, require a smaller amount of additional energy to escape from the atom.
This property makes Ge more unstable at high temperatures and results in excessive reverse current.
Thus Si is a more widely used semi-conductive material.
Covalent Bonds
Si crystal : each atom positions itself with 4 adjacent Si atoms
A Si atom with its 4 valence electrons shares an electron with each of its four neighbours
Creates 8 shared valence electrons for each atom and produces a state of chemical stability
Sharing of valence electrons produces the covalent bonds that hold the atoms together
Covalent bonding for Ge is similar as has 4 valence electrons.
Bonding diagram:
red -ve represent the shared valence electrons. 
Covalent bonds in a Si crystal.