PN junctions are formed when a P-type semiconductor is joined to an N-type semiconductor. In a PN junction, the region near the junction becomes depleted of free charge carriers as holes from the P-region combine with electrons from the N-region. A PN junction can be forward or reverse biased depending on whether the positive terminal of a battery is connected to the P-region or N-region. When forward biased, the potential barrier is reduced and current can flow. When reverse biased, the potential barrier increases and no current flows until the breakdown voltage is exceeded. The current-voltage characteristics of a PN junction show a linear increase in current under forward bias and sharply rising current under reverse bias or at high

1. PN JUNCTION
BY-MEHEDI HASAN
SARIK

2. WHAT IS PN JUNCTION
■ PN-junction:When P-type semiconductor is
suitably joined to N-tpye semiconductor,the
contact surface is calleed PN-junction.

3. N-TYPE SEMICONDUCTOR
■ N-Type: Whenasmallamountof pentavalent
impurity is added to a pure semiconductor,it’s known
as a N-type semiconductor.

4. P-TYPE SEMICONDUCTOR
■ P-type:when a small amount of trivalent
impurity is added to a pure semiconductor,it’s
called P-type semiconductor.

5. DEPLETION REGION
■ The depletion region, also called depletion layer,
depletionzone.Thecombiningof electronsand
holes depletes the holes in the P-region and the
electrons in the N-region near the junction.

6. BIASING APN-JUNCTION
■ In relation to a PN junction, there are two bias
condition:
Biasing a PN-junction
Forward biasing Reverse biasing

7. BATTERY CONNECTION
■ Forward Bias Mode: Positiveterminal
connected to P-region and negative terminal
connected to N-region.
■ Reverse bias mode: Negativeterminal
connected to P-region and positive terminal
connected to N-region.

8. FORWARD BIASING
■ When voltage is applied across adiode in such a
waythatthediodeallowscurrentandthe
potential barrier reduced, the diode is said to be
forward-biased.

9. REVERSE BIASING
■ When voltage is applied across a diode in such a
waythat the diode prohibits current and
potential barrier increase, the diode is said to be
reverse-biased.

10. V-I CHARACTERISTICSOF PN-J
UNCTION
The curve drawn between voltage across the junction along x
axis and current through the y axis.

11. IN FORW
ARD BIAS
■ No current flows until the barrier voltage (0.3 for Ge) is
overcome.
■ Then the curve has linear rise and the current increase
with the increase forward voltage.
■ Above the 3v, the majority carriers passing the junction
gain sufficient energy to knock out the electrons.
■ Therefore, the forward current increase sharply.

12. IN REVERSE BIAS
■ Junction resistance, potential barrier increase.
■ When reverse voltage is increased beyond a
value, called breakdown voltage.
■ Reverse current increase sharply.
■ Above 25 reverse voltage, destroys the junction
permanently.

13. ADVANTAGE
■ No filament is necessary.
■ Occupies lesser space.
■ Long life.

14. THANKSEVERYBODY