MEASUREMENT OF THE I-V PROPERTIES OF SEMICONDUCTOR DIODES
*Valynn Katrine P. Mag-usara and Editha P. Jacosalem
Department of Physics, MSU-IIT
9200 Iligan City
*Presentor
Abstract
Current-voltage (I-V) properties of semiconductor diodes like silicon detector diode and germanium
detector diode are determined using a 3-in-1 characterization apparatus at the MSU-IIT Materials Science
Research Laboratory. The behavior of the diode current ID with respect to the diode voltage VD is
investigated at room temperature to obtain cut-in voltage Vc, dynamic resistance rd, maximum reverse
current Io, and ideality factor or material constant . The results are found to be within the range of
accepted values.
Keywords: cut-in voltage, dynamic resistance, maximum reverse current, ideality factor/material constant
I. Introduction
qVD
ID = Io e kT 1 (1)
Semiconductors are materials that can
conduct better than an insulator but cannot
conduct electrons as well as a true conductor. In
where q is the electronic charge and is equal to
the form of electronic devices, they have played
1.602 x 10-19 coulombs, k is the Boltzmann
a vital role in the technological revolution of
constant with a value of 1.381 x 10-23 J/K and T
modern years [1]. The simplest among these
is the temperature in Kelvin [2]. The typical
devices are called semiconductor diodes which
current-voltage (I-V) curve of a semiconductor
are found in electronic systems such as television
diode is shown in Figure 1.
sets, portable radios, stereo equipment, and other
instruments where they are used to perform
numerous tasks.
Semiconductor diodes are made by joining
two different types of semiconductor materials in
a special way so that when a proper polarity
voltage is applied, electrons readily pass through
one material to the other. However, if the voltage
is reversed, there is very minimal electron flow.
In other words, a semiconductor diode allows
current to pass through when in forward bias,
and blocks current when in reverse bias. They
Figure 1. Typical semiconductor diode curve
also have properties or characteristics that enable
them to perform many different electronic
The aim of this study is to obtain I-V
functions.
measurements for semiconductor diodes, and to
The general characteristics of a
present it in graphical form to enable extraction
semiconductor diode can be defined by the ideal
of diode properties. More specifically, the
diode equation for forward and reverse bias
following properties are to be measured from the
regions which is given as
I-V curves defined by semiconductor diodes:
" cut-in voltage Vc, which is the forward-
bias voltage required to reach the region of
upward swing;
" dynamic resistance rd, which is the
resistance measured between the terminals
of a diode under specific voltages or
currents at a point of forward-bias
" maximum reverse current Io, which refers
to the small value of direct current that
flows when a semiconductor diode has a
reverse bias; and
Figure 2. Panel diagram of the apparatus
" material constant or ideality factor ,
which plays a part in determining the shape
From every set of current-voltage readings,
of the I-V curve at low current levels [2].
two plots can be produced: a plot of current vs.
This factor varies between 1 (for pure
voltage, and a plot of the natural logarithm of
germanium) and 2 (for pure silicon),
current (ln I) vs. voltage [4]. Through careful
depending on the physical construction and
analysis of these plots, the diode properties Vc,
the purity of the semiconductor .
rd, , and Io can be determined.
The cut-in voltage Vc is obtained by
It is to be noted that the cut-in voltage values
extending the linear portion of the current vs.
for silicon diodes lie somewhere between 0.3
voltage plot. The dynamic resistance rd, on the
volts to 0.7 volts, while that of germanium
other hand, defines the slope of the linear portion
diodes are expected to be from 0.1 volts to 0.3
and is expressed as
volts [3]. It is also not uncommon for a
VD
germanium diode to have a maximum reverse
rd = [5]. (2)
current in the order of 1µA or 2µA at 25°C. The
ID
typical values of the reverse maximum current
From the ln I vs. voltage plot, graphical
for silicon, however, are much lower than that of
extraction of the maximum reverse current Io and
germanium for similar voltage and current levels.
It is also to be expected further that for an I-V material constant can be done.
plot with a steep slope for its linear portion, a By taking the natural logarithm of the ideal
small value of dynamic resistance is likely to be diode equation, the expression becomes
obtained [2].
qV
ln ID = ln Io + . (3)
kT
II. Methodology
Thus, when ln I and V are plotted, a line is
In this study, the experimental unit used is a
obtained. The y-intercept of the line defines ln Io
3-in-1 apparatus which consists of the following
and the slope gives the value of the material
subsystems: an integrated circuit-regulated
constant , i.e.
variable voltage supply in the range 0-9 volts
(V); a 3 ½ digital voltmeter with a basic
q VD
= [6]. (4)
sensitivity of 100mV to measure voltage; and a
kT ln ID
set of suitable precision resistances (1 ohm ( ),
100 , and 10K ) to enable current
measurements in the range 10 nanoamperes (nA)
III. Results and Discussion
to 100 mA.
The apparatus allows measurement of the
Current-voltage measurements are taken at
diode current vs. diode voltage both in forward
room-temperature (25°C) for a silicon detector
bias and reverse bias. As the voltage across the
diode and a germanium detector diode.
circuit is increased in small steps, the diode
The data acquired are plotted using gnuplot to
current and the diode voltage are obtained.
produce the current-voltage curves found in
Figure 4. From these curves, the Vc and rd of the
silicon detector diode and the germanium
detector diode are obtained.
For the silicon detector diode, the cut-in I-V and ln I-V plots for silicon and germanium
voltage Vc is found to be at 0.556V and the detector diodes. The obtained results were found
to be within the range of accepted values for
dynamic resistance rd is at 54.18 . As for the
silicon and detector diodes. Accordingly, the
germanium detector diode, a value of 0.171V is
silicon detector diode has a higher cut-in voltage
obtained for Vc and the dynamic resistance rd is
than the germanium detector diode. In terms of
found to be at 46.61 .
the maximum reverse current, the silicon diode is
A plot of the ln I-V curves of the diode
more ideal because the results show that it allows
samples is presented in Figure 5. Appropriate
lesser current to pass through under reverse bias.
linear functions are fitted to the curves and from
In addition, the sensitivity/capability of the
the defined plot, the diode properties Io and are
apparatus imposes limitations as it cannot
obtained.
display the corresponding value for the
maximum reverse current Io accurately.
However, a specific value of Io for a diode can
still be obtained analytically from the ln I vs.
voltage plot. Moreover, measurement of the I-V
properties of other samples such as light emitting
diodes (LEDs), photodiodes, zener diodes, and
laboratory-prepared semiconductor diodes are
yet to be done.
Acknowledgments
The authors express their utmost gratitude to
the Department of Science and Technology 
Figure 4. Current-voltage (I-V) plot
Philippine Council for Advanced Science and
Technology Research and Development (DOST-
The maximum reverse current Io of the silicon
PCASTRD) for the equipment. Thanks is also
detector diode is found to be at 0.00000286mA
due to Dr. Angelina Bacala, Mr. Lowell
(or 0.00286µA) and the material constant is
Pamatong, Mr. Jingle Magallanes, Prof.
1.87. For the germanium detector diode, the
Reynaldo Vequizo, the Senior BS Physics
values obtained are 0.00163mA (or 1.63µA) and
students and the Materials Science Group of
1.37 for the Io and , respectively. MSU-IIT for their support and advice.
References
[1] Miller, M. H., Introductory Electronics
Notes, University of Michigan  Dearborn,
2000.
[2] Boylestad, R. and L. Nashelsky, Electronic
Devices and Circuit Theory, USA: Prentice
Hall, Inc., 1997.
[3] Electronic Principles, 6th Edition, Malvino
Inc., 1998.
[4] Wasseman, M., I-V Characteristic of
Semiconductor Diodes,
http://www.Educators
Figure 5. ln current-voltage (ln I-V) plot
Corner.com/experiments, INTERNET.
[5] User s Manual: Characteristics of
Conclusion
Semiconductor Diodes, pp 1-4.
[6] User s Manual: Study of P-N Junction,
The cut-in voltage Vc, dynamic resistance rd,
pp 1-2.
maximum reverse current Io, and material
constant or ideality factor were measured from