University of Information Technology and Sciences
Lab Report
Submitted To
Ayanava Paul
Lecturer
Course Title: Electronic Devices and Circuits Lab
Course Code: EEE252
Semester: Autumn-22, Batch:51(2C)
Submitted By
Nusrat Jahan
ID: 2215151114
Date of Submission : 17 October 2022
Experiment No: 01
Experiment Name: Determination of the characteristic
curve of a Diode.
Theory:
It is the simplest of semiconductor devices but plays a very vital role in
electronic systems, having
characteristics that closely match those of a simple switch. The ideal diode is a
two-terminal device
formed from a junction of n-type and p-type semiconductor material. The lead
connected to the p-type
material is called the anode and the lead connected to the n-type material is the
cathode. In general, the
cathode of a diode is marked by a solid line on the diode. It has low (ideally
zero) resistance to the flow of
current in one direction, and high (ideally infinite) resistance in the other
direction.
A diode is made of a crystal of semiconductor, usually silicon, but germanium
and gallium arsenide are
also used. Impurities are added to it to create a region on one side that contains
negative charge carriers
(electrons), called an n-type semiconductor, and a region on the other side that
contains positive charge
carriers (holes), called a p-type semiconductor. P-type of semiconducting
material is made by defusing
impurity of trivalent type of material in the pure form of semiconductor.N-type
semiconducting material is made by defusing impurity of pentavalent type of
material in the pure form of semiconductor.
When the n-type and p-type materials are attached together, a momentary flow
of electrons occur from the n to the p side resulting in a third region between the
two where no charge carriers are present. This
region is called the depletion region because there are no charge carriers (neither
electrons nor holes) in it.
The diode's terminals are attached to the n-regions and p-regions. The boundary
between these two
regions, called a p–n junction, is where the action of the diode takes place.
When the diode is forward biased, due to the negative terminal on the n-side,
electrons from the n-side are pushed towards the p-region. Similarly, due to
positive voltage on the p-side of the diode, Holes from the p-region are pushed
towards n-side. Due to this the electrons will start converting the positive ions in
the p-region into neutral atoms and holes will start converting the negative ions
in the n-region to neutral
atoms. Hence width of the depletion region starts reducing due to reduction in
the barrier potential. This
keeps happening and at a certain point the depletion region collapses and there
is no opposition to the
flow of current. Hence large number of electrons and holes will cross the
junction and make the current to flow from anode to cathode. Hence, forward
biased electrical resistance of diode is very small and hence there is a small
voltage drop (Practical condition, ideally there should be 0 forward resistance)
across it. Its value for silicon diode is about 0.7 V. Thus, the p-n junction diode
will allow a current to pass through it only when it is forward biased.
When the diode is reversed biased the hole from the p-side will get attracted
towards the negative terminal of the supply and electrons from the n-side are
attracted towards the positive terminal. Hence the process of widening of the
depletion region takes place and hence more and more opposition to the flow of
current takes place. Hence, ideally the reverse biased resistance of the diode is
infinite and no current flows from the diode when it is reversed biased. Due to
large reverse biased voltage, suddenly large current will flow through the
reverse biased voltage. Due to this large power gets dissipated in the diode
which may damage it permanently. In zero bias condition no voltage is applied
and no current flows
through the diode. So, the diode remains in the cut-off region. Operation of
diode can be summarized in
form of ID-V diode characteristics graph.
Circuit Diagram:
Figure 1: Circuit Diagram of the experiment.
Data Table:
Data table for Diode Characteristic:
V
VD
ID
0.300V
0.300V
0.0mA
0.400V
0.395V
0.0mA
0.500V
0.455V
0.0452mA
0.600V
0.480V
0.12mA
0.700V
0.494V
0.206mA
Graph:
Figure 2: ID-V characteristics in diode.
Discussion:
1. We used create circuit in TinkerCAD and then simulate our circuit,
and observed the voltage drop accross the diode,as well as the
current through the diode.
2. We put the diode in forward bias and used a variable DC power
supply to vary the supplied voltage, V
3. We varied the voltage from 0.3 to 0.7 volts.
4. We get ID and VD from the data table.
5. We put both ID and VD into the graph.
6. The graph shows that the curve goes up from the 0.5 volts.
7. The line gradually moves straight along the direction of ID when the
value of VD is 0.7 volts.