Slide on PN junction...BY Mehedi Hasan Sarik.. Daffodil International University (bd) CSE Department.

1. PN JUNCTIONPN JUNCTION
BY-MEHEDI HASANBY-MEHEDI HASAN
SARIKSARIK

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

3. N-TYPE SEMICONDUCTORN-TYPE SEMICONDUCTOR
 N-TypeN-Type: When a small amount of pentavalent: When a small amount of pentavalent
impurity is added to a pure semiconductor,it’s knownimpurity is added to a pure semiconductor,it’s known
as a N-type semiconductor.as a N-type semiconductor.

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

5. DEPLETION REGIONDEPLETION REGION
 TheThe depletion regiondepletion region, also called, also called depletion layerdepletion layer,,
depletion zonedepletion zone.The combining of electrons and.The combining of electrons and
holes depletes the holes in the P-region and theholes depletes the holes in the P-region and the
electrons in the N-region near the junction.electrons in the N-region near the junction.

6. BIASING A PN-JUNCTIONBIASING A PN-JUNCTION
 In relation to a PN junction, there are two biasIn relation to a PN junction, there are two bias
condition:condition:
Biasing a PN-junction
Forward biasing Reverse biasing

7. BATTERY CONNECTIONBATTERY CONNECTION
 Forward Bias ModeForward Bias Mode:: Positive terminalPositive terminal
connected to P-region and negative terminalconnected to P-region and negative terminal
connected to N-region.connected to N-region.
 Reverse bias modeReverse bias mode: Negative terminal
connected to P-region and positive terminal
connected to N-region.

8. FORWARD BIASINGFORWARD BIASING
 When voltage is applied across a diode in such aWhen voltage is applied across a diode in such a
way that the diode allows current and theway that the diode allows current and the
potential barrier reduced, the diode is said to bepotential barrier reduced, the diode is said to be
forward-biasedforward-biased..

9. REVERSE BIASINGREVERSE BIASING
 When voltage is applied across a diode in such aWhen voltage is applied across a diode in such a
way that the diode prohibits current andway that the diode prohibits current and
potential barrier increase, the diode is said to bepotential barrier increase, the diode is said to be
reversereverse-biased.-biased.

10. V-I CHARACTERISTICS OF PN-JUNCTIONV-I CHARACTERISTICS OF PN-JUNCTION
The curve drawn between voltage across the junction along xThe curve drawn between voltage across the junction along x
axis and current through the y axis.axis and current through the y axis.

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

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

13. ADVANTAGEADVANTAGE
 No filament is necessary.No filament is necessary.
 Occupies lesser space.Occupies lesser space.
 Long life.Long life.

14. THANKS EVERYBODYTHANKS EVERYBODY