Capitulo 1:

Diodos Semiconductores
 1.2 Diodos
El diodo es un dispositivo
de 2 terminales.

Un diodo ideal conduce en

una sola dirección.

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 Diode Characteristics
Región Conducción Región No Conducción

• The voltage across the diode is 0 V • All of the voltage is across the diode
• The current is infinite • The current is 0 A
• The forward resistance is defined as • The reverse resistance is defined as
RF = VF / IF RR = VR / IR
• The diode acts like a short • The diode acts like open

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 1.3 Semiconductor Materials

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 1.3 Semiconductor Materials

Materials commonly
used in the • Silicon (Si)
development of • Germanium (Ge)
semiconductor • Gallium Arsenide (GaAs)
devices.

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 1.3 Semiconductor Materials

Estructura cristalina de un
semiconductor intrínseco, compuesta
solamente por átomos de silicio (Si)
que forman una celosía. Como se
puede observar en la ilustración, los
átomos de silicio (que sólo poseen
cuatro electrones en la última órbita o
banda de valencia), se unen formando
enlaces covalente para completar
ocho electrones y crear así un cuerpo
sólido semiconductor. En esas
condiciones el cristal de silicio se
comportará igual que si fuera un
cuerpo aislante.

Electronic Devices and Circuit Theory, 10/e Copyright ©2009 by Pearson Education, Inc.
Robert L. Boylestad and Louis Nashelsky Upper Saddle River, New Jersey 07458 • All rights reserved.
 1.4 Niveles de Energía

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1.4 Niveles
de Energía

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 1.5 Materiales Extrínsecos
The electrical characteristics of silicon and germanium are improved
by adding materials in a process called doping.
n-type
There are just two types of doped semiconductor materials:
p-type

• n-type materials contain an excess of conduction band electrons.

• p-type materials contain an excess of valence band holes.

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 Majority and Minority Carriers
Two currents through a diode:

Majority Carriers

• The majority carriers in n-type materials are electrons.

• The majority carriers in p-type materials are holes.

Minority Carriers

• The minority carriers in n-type materials are holes.

• The minority carriers in p-type materials are electrons.

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 1.6 Diodo Semiconductor

p-n Junctions
One end of a silicon or germanium crystal can be doped as a p-
type material and the other end as an n-type material.

The result is a p-n junction.

junction

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 p-n Junctions
At the p-n junction, the excess
conduction-band electrons on the
n-type side are attracted to the
valence-band holes on the p-type
side.

The electrons in the n-type

material migrate across the
junction to the p-type material
(electron flow).
The result is the formation of a
The electron migration results in depletion region around the
a negative charge on the p-type junction.
side of the junction and a positive
charge on the n-type side of the
junction.

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 Diode Operating Conditions

A diode has three operating conditions:

• No bias
• Forward bias
• Reverse bias

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 Diode Operating Conditions

No Bias
• No external voltage is applied: VD = 0 V
• No current is flowing: ID = 0 A
• Only a modest depletion region exists

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 Diode Operating Conditions
Reverse Bias
External voltage is applied across the p-n junction in
the opposite polarity of the p- and n-type materials.

• The reverse voltage causes the

depletion region to widen.
• The electrons in the n-type material
are attracted toward the positive
terminal of the voltage source.
• The holes in the p-type material are
attracted toward the negative terminal
of the voltage source.

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 Diode Operating Conditions
Forward Bias
External voltage is applied across the p-n junction in
the same polarity as the p- and n-type materials.

• The forward voltage causes the

depletion region to narrow.
• The electrons and holes are pushed
toward the p-n junction.
• The electrons and holes have sufficient
energy to cross the p-n junction.

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 Actual Diode Characteristics
Note the regions for no
bias, reverse bias, and
forward bias conditions.

Carefully note the scale

for each of these
conditions.

ID = IS(ekVD/Tk -1)

ID = ISekVD/Tk -IS

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 Zener Region
The Zener region is in the diode’s
reverse-bias region.
At some point the reverse bias voltage
is so large the diode breaks down and
the reverse current increases
dramatically.
• The maximum reverse voltage that won’t
take a diode into the zener region is
called the peak inverse voltage or peak
reverse voltage.
voltage
• The voltage that causes a diode to enter
the zener region of operation is called the
zener voltage (VZ).

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 Forward Bias Voltage
The point at which the diode changes from no-bias condition
to forward-bias condition occurs when the electrons and
holes are given sufficient energy to cross the p-n junction.
This energy comes from the external voltage applied across
the diode.

The forward bias voltage required for

a:

• gallium arsenide diode  1.2 V

• silicon diode  0.7 V
• germanium diode  0.3 V

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 Temperature Effects

As temperature increases it adds energy to the diode.

• It reduces the required forward bias voltage for forward-
bias conduction.
• It increases the amount of reverse current in the reverse-
bias condition.
• It increases maximum reverse bias avalanche voltage.
Germanium diodes are more sensitive to temperature
variations than silicon or gallium arsenide diodes.

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 Resistance Levels
Semiconductors react differently to DC and AC currents.

There are three types of resistance:

• DC (static) resistance
• AC (dynamic) resistance
• Average AC resistance

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 DC (Static) Resistance

For a specific applied DC voltage

VD, the diode has a specific
current ID, and a specific
resistance RD.

VD
RD 
ID

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 AC (Dynamic) Resistance
In the forward bias region:

26 mV
rd   rB
ID

• The resistance depends on the amount of current (ID) in the diode.

• The voltage across the diode is fairly constant (26 mV for 25C).
• rB ranges from a typical 0.1  for high power devices to 2  for low
power, general purpose diodes. In some cases rB can be ignored.

In the reverse bias region:

rd  

The resistance is effectively infinite. The diode acts like an open.

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 Average AC Resistance

ΔVd
rav  pt. to pt.
ΔI d

AC resistance can be
calculated using the current
and voltage values for two
points on the diode
characteristic curve.

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 Diode Equivalent Circuit

Modelo de segmento lineales

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 Diode Equivalent Circuit

Modelo simplificado

Electronic Devices and Circuit Theory, 10/e Copyright ©2009 by Pearson Education, Inc.
Robert L. Boylestad and Louis Nashelsky Upper Saddle River, New Jersey 07458 • All rights reserved.
 Diode Equivalent Circuit

Dispositivo ideal

Electronic Devices and Circuit Theory, 10/e Copyright ©2009 by Pearson Education, Inc.
Robert L. Boylestad and Louis Nashelsky Upper Saddle River, New Jersey 07458 • All rights reserved.
 Diode Specification Sheets
Data about a diode is presented uniformly for many different diodes.
This makes cross-matching of diodes for replacement or design
easier.
1. Forward Voltage (VF) at a specified current and temperature
2. Maximum forward current (IF) at a specified temperature
3. Reverse saturation current (IR) at a specified voltage and
temperature
4. Reverse voltage rating, PIV or PRV or V(BR), at a specified
temperature
5. Maximum power dissipation at a specified temperature
6. Capacitance levels
7. Reverse recovery time, trr
8. Operating temperature range

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 Diode Capacitance

In reverse bias, the depletion layer is very large. The diode’s strong positive and
negative polarities create capacitance, CT. The amount of capacitance depends
on the reverse voltage applied.

In forward bias storage capacitance or diffusion capacitance (C D) exists as the

diode voltage increases.

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 Reverse Recovery Time (trr)

Reverse recovery time is the time required for a diode to stop

conducting once it is switched from forward bias to reverse bias.

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 1.13 Diode Symbol and Packaging

The anode is abbreviated A

The cathode is abbreviated K

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 Diode Testing

Diode checker
Ohmmeter
Curve tracer

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 Diode Checker

Many digital multimeters have a diode checking function.

The diode should be tested out of circuit.

A normal diode exhibits its forward voltage:

• Gallium arsenide  1.2 V

• Silicon diode  0.7 V
• Germanium diode  0.3 V

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 Ohmmeter
An ohmmeter set on a low Ohms scale can be used to test a
diode. The diode should be tested out of circuit.

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 Curve Tracer
A curve tracer displays the characteristic curve of a diode in the
test circuit. This curve can be compared to the specifications of
the diode from a data sheet.

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 Other Types of Diodes

Zener diode
Light-emitting diode
Diode arrays

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 Zener Diode

A Zener is a diode operated in reverse bias

at the Zener voltage (VZ).

Common Zener voltages are between 1.8 V

and 200 V

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 Light-Emitting Diode (LED)

An LED emits photons when it is forward biased.

These can be in the infrared or visible spectrum.
The forward bias voltage is usually in the range of 2 V to 3 V.

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 Diode Arrays
Multiple diodes can be
packaged together in an
integrated circuit (IC).
Common Anode

A variety of combinations
exist. Common Cathode

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Electronic Devices and Circuit Theory, 10/e Copyright ©2009 by Pearson Education, Inc.
Robert L. Boylestad and Louis Nashelsky Upper Saddle River, New Jersey 07458 • All rights reserved.