overview of electronic devices

1. KARPAGAM INSTITUTE OF
TECHNOLOGY, COIMBATORE-105
EC 8252 & ELECTRONIC DEVICES
Presented b y
Dr.S.SYED JAMAESHA
AP/ECE
Karpagam insttute of technology

2. Syllabus
UNIT I SEMICONDUCTOR DIODE
PN junction diode, Current equations, Energy Band diagram, Diffusion
and drift current densities, forward and reverse bias characteristics,
Transition and Diffusion Capacitances, Switching Characteristics,
Breakdown in PN Junction Diodes.

3. Semiconductors
• Pure semiconductors
– thermal vibration results in some bonds being broken
generating free electrons which move about
– these leave behind holes which accept electrons from
adjacent atoms and therefore also move about
– electrons are negative charge carriers
– holes are positive charge carriers
• At room temperatures there are few charge
carriers
– pure semiconductors are poor conductors
– this is intrinsic conduction

4. Semiconductors
• When p-type and n-type materials are joined
this forms a pn junction
– majority charge carriers on each side diffuse
across the junction where they combine with (and
remove) charge carriers of the opposite polarity
– hence around the junction there are few free
charge carriers and we have a depletion layer
(also called a space-charge layer

5. PN DIODE
• The diffusion of positive
charge in one direction
and negative charge in
the other produces a
charge imbalance
– this results in a potential
barrier across the
junction

6. Potential barrier
– the barrier opposes the flow of majority charge
carriers and only a small number have enough
energy to surmount it
• this generates a small diffusion current
– the barrier encourages the flow of minority
carriers and any that come close to it will be swept
over
• this generates a small drift current
– for an isolated junction these two currents must
balance each other and the net current is zero

7. Forward bias
– if the p-type side is made positive with respect to
the
n-type side the height of the barrier is reduced
– more majority charge carriers have sufficient
energy to surmount it
– the diffusion current therefore increases while the
drift current remains the same
– there is thus a net current flow across the junction
which increases with the applied voltage

8. • Reverse bias
– if the p-type side is made negative with respect to the
n-type side the height of the barrier is increased
– the number of majority charge carriers that have
sufficient energy to surmount it rapidly decreases
– the diffusion current therefore vanishes while the drift
current remains the same
– thus the only current is a small leakage current caused
by the (approximately constant) drift current
– the leakage current is usually negligible (a few nA)

9. UNIT-2
BIPOLAR JUNCTION Transistors

10. Bipolar Junction Transistors (BJT)

11. BJT Cross-Sections

12. Common-Emitter NPN Transistor

13. Input Characteristics

14. TUNNEL DIODE (Esaki Diode)
• It was introduced by Leo Esaki in 1958.
• Heavily-doped p-n junction
– Impurity concentration is 1 part in 10^3 as compared to 1
part in 10^8 in p-n junction diode
• Width of the depletion layer is very small
(about 100 A).
• It is generally made up of Ge and GaAs.
• It shows tunneling phenomenon.
• Circuit symbol of tunnel diode is :

15. SCR
• The SCR had its roots in the 4-layer diode. By
adding a gate connection, the SCR could be
triggered into conduction. This improvement
made a much more useful device than the 4-
layer diode

16. • SCRs are used in a variety of power control
applications. One of the most common
applications is to use it in ac circuits to control
a dc motor or appliance because the SCR can
both rectify and control.

17. The UnijunctioUJTUJTn Transistor (UJT• The UJT consists of a a block of lightly-doped
(high resistance) n-material with a p-material
grown into its side. It is often used as a trigger
device for SCRs and triacs

18. Thank you