For More Visit : www.LearnEngineering.in
EC3353 - ELECTRON DEVICES AND CIRCUITS
R2021
n
g.i
rin
ee
gin
UNIT I
PN DIODE AND ITS APPLICATIONS
En
arn
Le
w.
ww
For More Visit : www.LearnEngineering.in
,For More Visit : www.LearnEngineering.in
INTRODUCTION
The current-voltage characteristics is of prime concern in the study of semiconductor devices
with light entering as a third variable in optoelectronics devices.The external characteristics of
the device is determined by the interplay of the following internal variables:
1. Electron and hole currents
2. Potential
3. Electron and hole density
4. Doping
.in
5. Temperature
Semiconductor equations
ng
The semiconductor equations relating these variables are given below:
eri
Carrier density:
e
gin
En
where is the electron quasi Fermi level and is the hole quasi Fermi level. These two
equations lead to
arn
In equilibrium = = Constant
Le
Current:
w.
There are two components of current; electron current density and hole current density .
There are several mechanisms of current flow:
ww
(i) Drift
(ii) Diffusion
(iii) thermionic emission
(iv) tunneling
For More Visit : www.LearnEngineering.in
,For More Visit : www.LearnEngineering.in
The last two mechanisms are important often only at the interface of two different materials such
as a metal-semiconductor junction or a semiconductor-semiconductor junction where the two
semiconductors are of different materials. Tunneling is also important in the case of PN junctions
where both sides are heavily doped.
In the bulk of semiconductor , the dominant conduction mechanisms involve drift and diffusion.
.in
The current densities due to these two mechanisms can be written as
ng
eri
where are electron and hole mobilities respectively and are their diffusion
constants.
Potential:
e
gin
The potential and electric field within a semiconductor can be defined in the following ways:
En
arn
Le
All these definitions are equivalent and one or the other may be chosen on the basis of
w.
convenience.The potential is related to the carrier densities by the Poisson equation: -
ww
where the last two terms represent the ionized donor and acceptor density.
Continuity equations
These equations are basically particle conservation equations:
For More Visit : www.LearnEngineering.in
, For More Visit : www.LearnEngineering.in
Where G and R represent carrier generation and recombination rates.Equations (1-8) will form
the basis of most of the device analysis that shall be discussed later on. These equations require
models for mobility and recombination along with models of contacts and boundaries.
.in
Analysis Flow
ng
Like most subjects, the analysis of semiconductor devices is also carried out by starting from
simpler problems and gradually progressing to more complex ones as described below:
(i) Analysis under zero excitation i.e. equilibrium.
eri
(ii) Analysis under constant excitation: in other words dc or static characteristics.
(iii) Analysis under time varying excitation but with quasi-static approximation dynamic
characteristics.
e
(iv) Analysis under time varying excitation: non quasi-static dynamic characteristics.
gin
En
arn
Even though there is zero external current and voltage in equilibrium, the situation inside the
device is not so trivial. In general, voltages, charges and drift-diffusion current components at
any given point within the semiconductor may not be zero.
Le
w.
ww
For More Visit : www.LearnEngineering.in
EC3353 - ELECTRON DEVICES AND CIRCUITS
R2021
n
g.i
rin
ee
gin
UNIT I
PN DIODE AND ITS APPLICATIONS
En
arn
Le
w.
ww
For More Visit : www.LearnEngineering.in
,For More Visit : www.LearnEngineering.in
INTRODUCTION
The current-voltage characteristics is of prime concern in the study of semiconductor devices
with light entering as a third variable in optoelectronics devices.The external characteristics of
the device is determined by the interplay of the following internal variables:
1. Electron and hole currents
2. Potential
3. Electron and hole density
4. Doping
.in
5. Temperature
Semiconductor equations
ng
The semiconductor equations relating these variables are given below:
eri
Carrier density:
e
gin
En
where is the electron quasi Fermi level and is the hole quasi Fermi level. These two
equations lead to
arn
In equilibrium = = Constant
Le
Current:
w.
There are two components of current; electron current density and hole current density .
There are several mechanisms of current flow:
ww
(i) Drift
(ii) Diffusion
(iii) thermionic emission
(iv) tunneling
For More Visit : www.LearnEngineering.in
,For More Visit : www.LearnEngineering.in
The last two mechanisms are important often only at the interface of two different materials such
as a metal-semiconductor junction or a semiconductor-semiconductor junction where the two
semiconductors are of different materials. Tunneling is also important in the case of PN junctions
where both sides are heavily doped.
In the bulk of semiconductor , the dominant conduction mechanisms involve drift and diffusion.
.in
The current densities due to these two mechanisms can be written as
ng
eri
where are electron and hole mobilities respectively and are their diffusion
constants.
Potential:
e
gin
The potential and electric field within a semiconductor can be defined in the following ways:
En
arn
Le
All these definitions are equivalent and one or the other may be chosen on the basis of
w.
convenience.The potential is related to the carrier densities by the Poisson equation: -
ww
where the last two terms represent the ionized donor and acceptor density.
Continuity equations
These equations are basically particle conservation equations:
For More Visit : www.LearnEngineering.in
, For More Visit : www.LearnEngineering.in
Where G and R represent carrier generation and recombination rates.Equations (1-8) will form
the basis of most of the device analysis that shall be discussed later on. These equations require
models for mobility and recombination along with models of contacts and boundaries.
.in
Analysis Flow
ng
Like most subjects, the analysis of semiconductor devices is also carried out by starting from
simpler problems and gradually progressing to more complex ones as described below:
(i) Analysis under zero excitation i.e. equilibrium.
eri
(ii) Analysis under constant excitation: in other words dc or static characteristics.
(iii) Analysis under time varying excitation but with quasi-static approximation dynamic
characteristics.
e
(iv) Analysis under time varying excitation: non quasi-static dynamic characteristics.
gin
En
arn
Even though there is zero external current and voltage in equilibrium, the situation inside the
device is not so trivial. In general, voltages, charges and drift-diffusion current components at
any given point within the semiconductor may not be zero.
Le
w.
ww
For More Visit : www.LearnEngineering.in
