1. Electronic Fundamental Muhammad Zahid
BS Regular
11 February, 17
Introduction to Electronic Fundamental
Lecture - 1
Electronic Fundamental Muhammad Zahid

2. MS (Electronics) in progress from PAF-KIET
Muhammad Zahid
MS (Electronics) in progress from PAF-KIET
Contact:

3. Grading Midterm Paper Final Term Paper 25 5 10 50 100
Assignments
Class Participation
Quizzes
Attendance
Final
Total 25 5 10 50
100
Midterm Paper
Three out of five questions
Final Term Paper
Five out of Eight questions

4. Electrical Charge

5. 1
Electrical Charge
A charge is an electrical properties that is associated with matter.
All matters are composed of atoms; all atoms consist of electrons, protons, and neutrons.
According to the classical Bohr model, atoms have a planetary type of structure that consists of a central nucleus surrounded by orbiting electrons.

6. Electrical Charge
Each type of atom has a certain number of electrons and protons that distinguishes it from the atoms of all other elements.
For example, hydrogen is the simplest atom which has one proton and one electron.

7. Electrical Charge
The electrons have negative charge while proton have positive charge. Like charges repel each other, while unlike charges attract.
The amount of charge on each electron or proton is 1.6 x 10-19C.
In their normal (or neutral) state, all atoms of a given element have the same number of electrons as protons; the positive charges cancel the negative charges, and the atom has a net charge of zero.

8. Electrical Charge
Electrons are arranged in particular shells around the nucleus. The arrangement is on the basis of 2n2. where n is the no of shell.
The outermost shell is called valance shell and it has the least force of attraction from all other shell.
An atom becomes charged when it gains or looses an electron. A charged atom is called an Ion.

9. Electrical Charge
Electrons in valance shell are called valence electrons.
These valence electrons contribute to chemical reactions and bonding within the structure of a material and determine its electrical properties.
When a valence electron gains sufficient energy from an external source, it can break free from its atom. This is the basis for conduction in materials.

10. Classification of Materials
In terms of electrical properties, materials can be classified into three groups on the basis of outermost electrons.
Conductors
Semiconductors
Insulators

11. Conductors
A conductor is a material that easily conducts electrical current. It has less than four electron in the outermost orbit.
The less the outer most electron and the more distance from nucleus, the best is the conductor. e.g. gold (Au), silver (Ag), copper (Cu).

12. Insulators
An insulator is a material that does not conduct electrical current under normal conditions. It has greater than four electron in the outermost orbit.
Most good insulators are compounds rather than single-element materials and have very high resistivity.
Examples of insulators are rubber, plastics, glass, mica, and quartz.

13. Semiconductors
A semiconductor is a material that is between conductors and insulator. A semiconductor in its pure (intrinsic) state is neither a good conductor nor a good insulator.
It has four electron in the outermost orbit.
Single-element semiconductors are arsenic (As), silicon (Si), and germanium (Ge).

14. Energy Level Diagram
The valence shell of an atom represents a band of energy levels and that the valence electrons are confined to that band.
When an electron acquires enough additional energy, it can leave the valence shell, become a free electron, and exist in what is known as the conduction band.
The difference in energy between the valence band and the conduction band is called an energy gap or band gap.

15. Energy Level Diagram
When an electron falls in the conduction band, the electron is free to move throughout the material and is not tied to any given atom.

16. Semiconductors Silicon and Germanium:-
Both silicon and germanium have the characteristic four valence electrons.

17. Semiconductors
The valence electrons in germanium are in the fourth shell while those in silicon are in the third shell, closer to the nucleus.
The germanium valence electrons are at higher energy levels than those in silicon and, therefore, require a smaller amount of additional energy to escape from the atom.
This property makes germanium more unstable at high temperatures
For these reasons, silicon is a more widely used semiconductive material.

18. Covalent Bonding
When atoms combine to form a solid, crystalline material, they arrange themselves in a symmetrical pattern. The atoms within the crystal structure are held together by covalent bonds.
A silicon (Si) atom with its four valence electrons shares an electron with each of its four neighbors.
This effectively creates eight shared valence electrons for each atom and produces a state of chemical stability.

19. Current in Semiconductors
An intrinsic (pure) silicon crystal at room temperature has sufficient heat (thermal) energy for some valence electrons to jump the gap from the valence band into the conduction band, becoming free electrons.
Free electrons are also called conduction electrons.

20. Current in Semiconductors
When an electron jumps to the conduction band, a vacancy is left in the valence band within the crystal. This vacancy is called a hole.
More the conduction electron more will be the hole, creating an electron-hole pairs.
Recombination occurs when a conduction-band electron loses energy and falls back into a hole in the valence band.

21. Electron and Hole Current
The application of voltage across a piece of intrinsic silicon will results in the attraction o f thermally generated free electrons in the conduction band toward the positive end.
This movement of free electrons is one type of current in a semiconductive material and is called electron current.

22. Electron and Hole Current
The holes created by the free electrons in valance band are still attached to their atoms and are not free to move randomly in the crystal structure as are the free electrons.
A valence electron can move into a nearby hole with little change in its energy level, thus leaving another hole where it came from.

23. Electron and Hole Current
Although current in the valence band is produced by valence electrons, it is called hole current to distinguish it from electron current in the conduction band.