Short Notes: Semiconductors in Electronic Device | Electronic Devices - Electronics and Communication Engineering (ECE) PDF Download

 Page 1


Semiconductors in Electronic Devices
Semiconductors are the foundation of mo dern electronic devices, enabling the functionalit y of com-
p o nen ts suc h as dio des, transistors, and in tegrated circuits. Their unique electrical prop erties, whic h lie
b e t w een those of conductors and insulators, mak e them essen tial for con trolling and pro cessing electrical
signals in v arious applications.
1. In t ro d uction to Semiconductors
Semiconductors are materials with electrical conductivit y b et w een that of conductors (e.g., metals) and
insulators (e.g., glass). Common semiconductor materials include silicon (Si) and germanium (G e), with
silicon b eing the most widely used due to its abundance and stable prop erties. Semiconductors can b e
engineered to conduct or insulate under sp ecific conditions, making them ideal for electronic devices.
2. T yp es of Semiconductors
Semiconductors are classified in to t w o main t yp es:
• In trinsic Semiconductors : Pure semiconductors with no impurities. Their conductivit y dep ends
on thermally generated electron-hole pairs. The n um b er of c harge carrie rs is giv en b y:
n
i
=
v
N
c
N
v
e
-
Eg
2kT
where n
i
is the in trinsic carrier concen tration, N
c
and N
v
are the effectiv e densities of states in the
conduction and v alence bands, E
g
is the bandgap energy , k is Boltzmann’s constan t, and T is the
temp erature in Kelvin.
• Extrinsic Semiconductors : Dop ed with impurities to enhance conductivit y . They are further
divided in to:
– n-t yp e : Dop ed with p en ta v alen t impurities (e.g., phosphorus), in tro ducing extra electrons as
ma jorit y carriers.
– p-t yp e : Dop ed with triv alen t impurities (e.g., b oron), creating holes as ma jorit y carriers.
3. Energy Band Theory
The electrical prop erties of semiconductors are explained b y energy band theory:
• V alence Band : Filled with electrons at absolute zero.
• Conduction Band : Empt y at absolute z ero, where electrons can mo v e freely .
• Bandgap (E
g
) : The energy difference b et w een the v alence and conduction bands. F or silicon,
E
g
˜ 1.12 e V, and for germanium, E
g
˜ 0.67 e V.
Electrons can mo v e from the v alence band to the conduction band b y gaining energy (e.g., thermal or
optical), lea ving b ehind holes that act as p ositiv e c harge carriers.
4. Semiconductor Devices
Semiconductors are the basis for k ey electronic devices:
1
Page 2


Semiconductors in Electronic Devices
Semiconductors are the foundation of mo dern electronic devices, enabling the functionalit y of com-
p o nen ts suc h as dio des, transistors, and in tegrated circuits. Their unique electrical prop erties, whic h lie
b e t w een those of conductors and insulators, mak e them essen tial for con trolling and pro cessing electrical
signals in v arious applications.
1. In t ro d uction to Semiconductors
Semiconductors are materials with electrical conductivit y b et w een that of conductors (e.g., metals) and
insulators (e.g., glass). Common semiconductor materials include silicon (Si) and germanium (G e), with
silicon b eing the most widely used due to its abundance and stable prop erties. Semiconductors can b e
engineered to conduct or insulate under sp ecific conditions, making them ideal for electronic devices.
2. T yp es of Semiconductors
Semiconductors are classified in to t w o main t yp es:
• In trinsic Semiconductors : Pure semiconductors with no impurities. Their conductivit y dep ends
on thermally generated electron-hole pairs. The n um b er of c harge carrie rs is giv en b y:
n
i
=
v
N
c
N
v
e
-
Eg
2kT
where n
i
is the in trinsic carrier concen tration, N
c
and N
v
are the effectiv e densities of states in the
conduction and v alence bands, E
g
is the bandgap energy , k is Boltzmann’s constan t, and T is the
temp erature in Kelvin.
• Extrinsic Semiconductors : Dop ed with impurities to enhance conductivit y . They are further
divided in to:
– n-t yp e : Dop ed with p en ta v alen t impurities (e.g., phosphorus), in tro ducing extra electrons as
ma jorit y carriers.
– p-t yp e : Dop ed with triv alen t impurities (e.g., b oron), creating holes as ma jorit y carriers.
3. Energy Band Theory
The electrical prop erties of semiconductors are explained b y energy band theory:
• V alence Band : Filled with electrons at absolute zero.
• Conduction Band : Empt y at absolute z ero, where electrons can mo v e freely .
• Bandgap (E
g
) : The energy difference b et w een the v alence and conduction bands. F or silicon,
E
g
˜ 1.12 e V, and for germanium, E
g
˜ 0.67 e V.
Electrons can mo v e from the v alence band to the conduction band b y gaining energy (e.g., thermal or
optical), lea ving b ehind holes that act as p ositiv e c harge carriers.
4. Semiconductor Devices
Semiconductors are the basis for k ey electronic devices:
1
• Dio des : F ormed b y a p-n junction, allo wing curren t flo w in one direction. The curren t-v oltage
relationship is:
I = I
s
(
e
qV
kT
-1
)
whereI
s
is the saturation curren t,q is the electron c harge,V is the applied v oltage,k is Boltzmann’s
constan t, and T is the temp erature.
• T ransistors : Include Bip olar Junction T ransistors (BJT s) and Field-Effect T ransistors (FET s).
They amplify or switc h signals. F or a BJT, the collector curren t is :
I
C
= ßI
B
where ß is the curren t gain and I
B
is the base curren t.
• In tegrated Circuits (ICs) : Com bine m ultiple semiconductor devices on a single c hip, enabling
complex functions in micropro cessors, memory , and sensors.
5. Doping and Carrier Concen tration
Doping in tro duces impurities to con trol carrier concen tration:
• In n-t yp e semiconductors, the electron concen tration is appro ximately equal to the donor concen-
tration N
d
:
n˜ N
d
• In p-t yp e semiconductors, the hole concen tration is appro ximately equal to the acceptor concen-
tration N
a
:
p˜ N
a
• The pro duct of electron and hole concen trations satisfies:
np = n
2
i
6. Applications of Semiconductors
Semiconductors are in tegral to:
• Computing : Micropro cessors and memory c hips in computers and smartphones.
• Comm unications : RF transistors and dio des in wireless systems.
• P o w er Electronics : Dio des a nd MOSFET s in p o w er supplies and in v erters.
• Opto electronics : LEDs and photo detectors in displa ys and sensors.
7. Practical Considerations
• T emp erature Sensitivit y : Semiconductor conductivit y increases with temp erature due to more
electron-hole pairs, affecting device p erformance.
• Miniaturization : A dv ances in fabrication (e.g., CMOS tec hnology) allo w smaller, more e?icien t
devices but face c hallenges lik e quan tum effects.
2
Page 3


Semiconductors in Electronic Devices
Semiconductors are the foundation of mo dern electronic devices, enabling the functionalit y of com-
p o nen ts suc h as dio des, transistors, and in tegrated circuits. Their unique electrical prop erties, whic h lie
b e t w een those of conductors and insulators, mak e them essen tial for con trolling and pro cessing electrical
signals in v arious applications.
1. In t ro d uction to Semiconductors
Semiconductors are materials with electrical conductivit y b et w een that of conductors (e.g., metals) and
insulators (e.g., glass). Common semiconductor materials include silicon (Si) and germanium (G e), with
silicon b eing the most widely used due to its abundance and stable prop erties. Semiconductors can b e
engineered to conduct or insulate under sp ecific conditions, making them ideal for electronic devices.
2. T yp es of Semiconductors
Semiconductors are classified in to t w o main t yp es:
• In trinsic Semiconductors : Pure semiconductors with no impurities. Their conductivit y dep ends
on thermally generated electron-hole pairs. The n um b er of c harge carrie rs is giv en b y:
n
i
=
v
N
c
N
v
e
-
Eg
2kT
where n
i
is the in trinsic carrier concen tration, N
c
and N
v
are the effectiv e densities of states in the
conduction and v alence bands, E
g
is the bandgap energy , k is Boltzmann’s constan t, and T is the
temp erature in Kelvin.
• Extrinsic Semiconductors : Dop ed with impurities to enhance conductivit y . They are further
divided in to:
– n-t yp e : Dop ed with p en ta v alen t impurities (e.g., phosphorus), in tro ducing extra electrons as
ma jorit y carriers.
– p-t yp e : Dop ed with triv alen t impurities (e.g., b oron), creating holes as ma jorit y carriers.
3. Energy Band Theory
The electrical prop erties of semiconductors are explained b y energy band theory:
• V alence Band : Filled with electrons at absolute zero.
• Conduction Band : Empt y at absolute z ero, where electrons can mo v e freely .
• Bandgap (E
g
) : The energy difference b et w een the v alence and conduction bands. F or silicon,
E
g
˜ 1.12 e V, and for germanium, E
g
˜ 0.67 e V.
Electrons can mo v e from the v alence band to the conduction band b y gaining energy (e.g., thermal or
optical), lea ving b ehind holes that act as p ositiv e c harge carriers.
4. Semiconductor Devices
Semiconductors are the basis for k ey electronic devices:
1
• Dio des : F ormed b y a p-n junction, allo wing curren t flo w in one direction. The curren t-v oltage
relationship is:
I = I
s
(
e
qV
kT
-1
)
whereI
s
is the saturation curren t,q is the electron c harge,V is the applied v oltage,k is Boltzmann’s
constan t, and T is the temp erature.
• T ransistors : Include Bip olar Junction T ransistors (BJT s) and Field-Effect T ransistors (FET s).
They amplify or switc h signals. F or a BJT, the collector curren t is :
I
C
= ßI
B
where ß is the curren t gain and I
B
is the base curren t.
• In tegrated Circuits (ICs) : Com bine m ultiple semiconductor devices on a single c hip, enabling
complex functions in micropro cessors, memory , and sensors.
5. Doping and Carrier Concen tration
Doping in tro duces impurities to con trol carrier concen tration:
• In n-t yp e semiconductors, the electron concen tration is appro ximately equal to the donor concen-
tration N
d
:
n˜ N
d
• In p-t yp e semiconductors, the hole concen tration is appro ximately equal to the acceptor concen-
tration N
a
:
p˜ N
a
• The pro duct of electron and hole concen trations satisfies:
np = n
2
i
6. Applications of Semiconductors
Semiconductors are in tegral to:
• Computing : Micropro cessors and memory c hips in computers and smartphones.
• Comm unications : RF transistors and dio des in wireless systems.
• P o w er Electronics : Dio des a nd MOSFET s in p o w er supplies and in v erters.
• Opto electronics : LEDs and photo detectors in displa ys and sensors.
7. Practical Considerations
• T emp erature Sensitivit y : Semiconductor conductivit y increases with temp erature due to more
electron-hole pairs, affecting device p erformance.
• Miniaturization : A dv ances in fabrication (e.g., CMOS tec hnology) allo w smaller, more e?icien t
devices but face c hallenges lik e quan tum effects.
2
• Material Selection : Silicon dominates, but comp ound semiconductors (e.g., GaAs) are used for
high-frequency or opto electronic applications.
• Doping Precision : A ccurate doping is critical for consisten t device b eha vior.
8. F abrication T ec hniques
Semiconductor devices are man ufactured using pro cesses lik e:
• Doping : Ion implan tation or diffusion to in tro duce impurities.
• Photolithograph y : P atterning to create device structures.
• Epitaxy : Gro wing crystalline la y ers for high-qualit y semiconductors.
9. Conclusion
Semiconductors are the cornerstone of electronic devices, enabling the dev elopmen t of compact, e?icien t,
and v ersatile tec hnologies. Their abilit y to con trol electrical conductivit y through doping and band
structure manipulation mak es them indisp ensable in mo dern electronics. A dv ances in semiconductor
materials and fabrication con tin ue to driv e inno v ation in computing, comm unications, and b ey ond.
3