1. Semiconductors. Silicon crystal Types of semiconductors
Intrinsic semiconductors
Extrinsic semiconductors

2. Semiconductors Materials that are neither conductor nor insulator.
Element with 4 valance electrons is the best
semiconductor.
They contains free electrons.
Element with electrical properties between
those of conductors and insulators.

3. Difference between semiconductor and
conductor is because of the existence of
holes, present in semiconductors.
For example;
Germanium
Silicon

4. Silicon crystals As an insulator: As a conductor:
Perfect insulator at 25°C
8 valance electrons, covalently bonded with the
neighboring atoms.
As a conductor:
act as conductor at ambient temperature (above -273°C)
An electron gains energy, creating a vacancy in valence shell (hole), and move to bigger orbit. Hence, become a free electron.

5. Merging of free electron and a hole. Lifetime:
Recombination:
Merging of free electron and a hole.
Lifetime:
Amount of time for the creation and disappearance of free electron

6. Intrinsic semiconductor
Pure semiconductors.
Because of thermal energy, equal numbers
of electrons & holes are present.
These are often called as ‘carriers’
because they carry charge from one part
to another.
These holes & electrons move in opposite
direction.

7. Extrinsic semiconductor
Doped semiconductor is called extrinsic semiconductor.
Doping:
A way to increase conductivity of semiconductor.
Adding impurity atoms to intrinsic crystal to alter its conductivity.

8. Increasing free electrons:
Adding pantavalent atoms, e.g; Arsenic,
Antimony, Phosphorus
They are also called donar impurities,as they
donate an extra electron.
Greater the impurity added,
greater will be the
conductivity.
Lightly-doped semi-
conductors has high
resistance.
Heavily-doped semi-
conductors has low

9. Adding trivalent impurity, e.g; Aluminium, Boron,Gallium.
Increasing the holes:
Adding trivalent impurity, e.g; Aluminium, Boron,Gallium.
Also called acceptor atom, because hole can accept a free electron.

10. >N-TYPE SEMICONDUCTOR >P-TYPE SEMICONDUCTOR
>THE UNBIASED DIODE
>PN-JUNCTION
>DEPLETION LAYER

11. DEFRENCE BETWEEN INTRINSIC AND EXTRINSIC SEMICONDUCTORS

12. n-Type semiconductor 2 types of Extrinsic semiconductors
Doped with pantavalent impurity
‘n’ stands for negative
Majority carriers are free electrons
Minority carriers are the holes

13. p-Type semiconductor Doped with trivalent impurity
‘p’ stands for positive
Majority carriers are holes
Minority carriers are free electrons

14. Unbiased Diode Diode explains, two electrodes
It is electrically neutral
Also called junction diode or pn-crystal

15. pn-junction Border between p-type & n-type semiconductors.
Lead to inventions like, diode, transistors, & integrated circuits.

16. The depletion layer Free electrons diffuses from n-type to p-type,
converting the pentavalent atom in ‘n’ into positive ion and trivlent in ‘p’ into negative ion
Each pair of negative and positive ions at the
junction is called Dipole
This depreted region around the junction,
having no charges but only ions, is called
Depletion region

17. >BARRIER POTENTIAL & TEMPRATURE >FORWARD BIAS >REVERSE BIAS
BEENISH JAHANGIR
Roll#07-04
>BARRIER POTENTIAL & TEMPRATURE
>FORWARD BIAS
>REVERSE BIAS
>CURRENT IN REVERSE BIAS

18. Barrier Potential Electric field between positive and negative ions
Act as a barrier and causes no diffusion of free
electrons from ‘n’ to ‘p’
The electric field between ions is equivalent to
difference of potential
At 25°C the Barrier potential for; Germanium
Diode is 0.3V Silicon Diode is 0.7V

19. BARRIER POTENTIAL &TEMPERATURE
Junction temperature >Temperature inside the diode
Ambient temperature >Temperature outside the diode
Conducting diode>when Junction temperature is greater then Ambient temperature
>Less barrier potential at higher temperature
A barrier potential of a silicon diode decreases by 2mV for each degree celsius rise.
V/T=-2mV/°C

20. Forward bias DC source across diode
n-type connected to negative terminal of the
battery
p-type connected to positive terminal of the

21. Conduction of current is in forward direction
because of flow of free electron
No current if DC voltage is less then barrier
potential
Continuous current if DC voltage is greater then
barrier potential

22. Reverse bias n-type connected to positive terminal of the battery
p-type connected to negative terminal of the
negative terminal attracts the holes in ‘p’
Positive terminal attracts the free electrons in
‘n’

23. Depletion layer gets wider (because of ions
created around the junction )
Greater the reverse voltage greater will be
the potential

24. Current in reverse biased semiconductor
Saturation current
>A very small current because of minority
carriers and electron- hole pair inside the
depletion layer because of thermal energy..
Surface- leakage current
>Caused by surface impurity and imperfection in
the crystal
structure.
Approximately
ZERO current.

25. >ENERGY BAND IN INTRINSIC SEMICONDUCTOR >N-TYPE ENERGY BAND
>ENERGY LEVELS
>ENERGY BANDS
>ENERGY BAND IN INTRINSIC
SEMICONDUCTOR
>N-TYPE ENERGY BAND
>P-TYPE ENERGY BAND

26. ENERGY LEVELS Higher energy in larger orbit Electron gain energy when
lifted to larger orbit
Which has more potential
after lifting
This Energy is provided by
heat ,light and voltage
Falling electron radiate
light
Electron lose energy in
form of heat ,light,
radiation when falls to
lower orbit

27. ENERGY BANDS
Electron of an isolated silcon atom are bound to the neucleus having distinct energy level
In a solid, energy level of these isolated atom splits into sub-levels called discrete states
These states are so close that they appear
as a continuous energy band

28. A range of energy states between two consective
FORBIDDEN GAP
A range of energy states
between two consective
permissible energy bands
which cannot be occupied by
electron
VALANCE BAND
The energy band in the outer
most shell of an atom
occupying free electron
It is either completely or
partially filled but never
empty
Conduction is because of
movement of holes

29. CONDUCTION BAND Above the valance band Electron move freely
May be empty or partially filled
Conduction is because of movement of free electron
Bands below valance band take no part in conduction process because they are completely filled

30. ENERGY BAND IN INTRINSIC SEMICONDUCTOR
Partially filled conduction
& valance band
A narrow forbidden gap of
order 1eV between conduction
band & valance band

31. N-TYPE ENERGY BAND
P-TYPE ENERGY BAND

32. COMPARISON