Transcript SEMICONDUCTOR DEVICES

SEMICONDUCTOR
DEVICES
Diodes as a semiconductor devices
Diodes is made by joining p-types and ntypes semiconductor materials.
Diodes are undirectional devices that
allow current to flow through them only
in one direction.
Symbol and Structure
Biasing Diode
 There are two operating regions and three possible "biasing"
conditions for the standard Junction Diode and these are:
 Zero Bias - No external voltage potential is applied to the PNjunction.
 Reverse Bias - The voltage potential is connected negative, (-ve) to
the P-type material and positive, (+ve) to the N-type material across
the diode which has the effect of Increasing the PN-junction width.
 Forward Bias - The voltage potential is connected positive, (+ve) to
the P-type material and negative, (-ve) to the N-type material across
the diode which has the effect of Decreasing the PN-junction width.
Zero Biased
The potential barrier exists
discourages the diffusion of any
more majority carriers across the
junction.
The potential barrier helps minority
carriers (few free electrons in the Pregion and few holes in the Nregion) to drift across the junction.
Then an "Equilibrium" or balance
will be established when the
majority carriers are equal and both
moving in opposite directions, so
that the net result is zero current
flowing in the circuit. When this
occurs the junction is said to be in a
state of "Dynamic Equilibrium".
Reverse Biased
N material is connected to the
positive terminal of the voltage
source, V and the P material is
connected to the negative terminal of
the voltage source,V.The effect is that
charge carriers in both sections are
pulled away from the junction.Free
electrons on the N side are attracted
away from the junction because of the
attraction of the positive terminal of
the voltage source,V.Likewise,hole in
the P side are attracted away from
the junction because of the attraction
of the negative terminal of the voltage
source,V.Its will increases the
depletion region.
Forward Biased
N material is connected to the
negative terminal of the voltage
source, V and the P material is
connected to the positive terminal of
the voltage source,V.The voltage
source must be large enough to
overcome the internal barrier potential,
VB. The voltage source repels free
electrons in the N side across the
depletion zone and into the P side.
Once on the P side, the free electron
falls into a hole. The electron will then
travel from hole to hole as it is
attracted to the positive terminal of the
voltage source, V.
Its will decreases the depletion region.
I-V Characteristic Curve for silicon Diode
Zener Diode
Zener Diode symbol and I-V Characteristics
 Zener Diode is used in its
i. reverse bias or reverse breakdown mode


Diodes anode connects to the negative supply.
From the I-V characteristics its show that the zener diode has a region in
its reverse bias characteristics of almost a constant negative voltage
regardless of the value of the current flowing through the diode and
remains nearly constant even with large changes in current as long as
the zener diodes current remains between the breakdown current IZ(min)
and the maximum current rating IZ(max).

This ability to control itself can be used to great effect to regulate or
stabilise a voltage source against supply or load variations.Zener diode
will continue to regulate the voltage until the diodes current falls below
the minimum IZ(min) value in the reverse breakdown region.
Light Emitting Diodes
LED are the most visible type of diode, that emit a fairly narrow bandwidth of
either visible light at different coloured wavelengths, invisible infra-red light for
remote controls or laser type light when a forward current is passed through
them.
LED are semiconductor devices that convert electrical energy into light energy
Light emitting diodes are available in a wide range of colours with the most
common being RED(GaAsP), AMBER(GaAsP, YELLOW (GaAsPN) and
GREEN (AlGaP)
Biased Voltage
Biased voltage applied to transistor to operate successfully.
There are two type of biased voltage supplied to the transistor as a signal for it
operations. Two main condition in biasing a transistor are:
i. E-B(emitter-base) junction must be forward biased
ii. C-B (Collector –base )junction must be reverse biased
E
N
P
N
B
C
E
C
P
N
B
P
Bipolar Junction Transistor (BJT)
Like diode, BJTs are formed by P and N region and as we are already the point
at which P and N region join is known as a junction.
The bipolar junction transistor is a three terminal current operated
semiconductor device.
The terminals are called the emitter, base and collector. The emitter and
collector is made up of the same type of semiconductor material.
Figure above shows the structure and schematic symbol for NPN and PNP
transistor:
The arrow at the transistor symbol shows the direction of conventional current
when it is operates.
Either NPN or PNP, the base is very thin .Contains less majority current carrier.
Emitter functions as charge provider or majority current carrier in transistor.
Collector has to collect charge for circuit operates.
Base is the junction which is control the current flow.
Transistor Operation
E
N
P
- - - - - - - - - -
+
+
+
N
- - - - - - - - - -
C
B
E-B junction has been forward biased by V1, E-B junction will flow the
current because of electrons at emitter (N-type) will move by negative
potential supply V1. These electrons tried to go to positive potential V1
through base (P-type). But because of base only a thin layer and have small
amount of hole, not all electrons can flows. Only little electrons current can
flow at the base known as base current, IB.
IC
IE
IB
IE = IC + IB
The others electrons will collect at base layer in
large amount. Because of collector layer has
been connected to positive terminal of V2, the
positive potential will attracted that electrons flow
through collector as current collector, IC.