Intrinsic semiconductor, Concept of hole, p-type and n-type semiconductors are discussed. Lastly compensated semiconductor is introduced

1. ANIL NEERUKONDA INSTITUTE OF TECHNOLOGY &
SCIENCES(A)
Department of Electronics and Communication Engineering
ECE 125 Basic Electronics Engineering
 Academic year : 2022-23
 Class & Section : 1/4 ECE-A
 Name of the Faculty : Mr.D.Anil Prasad
ANIL PRASAD DADI/ECE/ANITS

2. UNIT-I(Semiconductor Diodes)
• Fermi level in Intrinsic & Extrinsic semiconductors. Mass-Action law.
Mobility and conductivity, Hall effect, Generation and recombination
of charges, Drift and diffusion current, Band structure of open-circuit
p-n junction, V-I characteristics, transition and diffusion capacitance,
reverse recovery time, Avalanche and zener breakdown, zener
diodes, Light Emitting Diodes.
ANIL PRASAD DADI/ECE/ANITS

3. Contents
• Intrinsic Semiconductors
• Hole as carrier transport in semiconductor
• Extrinsic Semiconductors
– n-type
– p-type
• Compensated semiconductor
ANIL PRASAD DADI/ECE/ANITS

4. Intrinsic Semiconductor
 A pure semiconductor is called Intrinsic Semiconductor.
 At T=00K no charge carriers are present in Conduction
band(CB). Valence band(VB) is filled with electron which are
tightly bound to nucleus. Hence at T=00K all semiconductor acts
as insulator.
 At T=3000K due to thermal energy the atoms in the crystal are
constantly vibrating, therefore they deform inter-atomic bonds.
Thus in some regions at some moments bonds may be
overstretched and bond energy may be smaller than thermal
energy.
ANIL PRASAD DADI/ECE/ANITS

5. Intrinsic Semiconductor
 Covalent bonds are broken and EHP are generated.
 Intrinsic semiconductor
 no of electrons= no of holes
ANIL PRASAD DADI/ECE/ANITS

6. Hole as a carrier transport in
semiconductor
• Hole is the absence of electron in covalent bond is called hole. The
current in the semiconductor is not only due to free electron in CB
but also due to valence electron in VB
• Bound electrons: The valence electrons taking part in the bonding
process is called bound electrons.
• The electrons already in the bonding process can participate in
conduction because of the presence of vacancies or holes.
• The bound electrons tend to move through vacancies and contribute
to current.
ANIL PRASAD DADI/ECE/ANITS

7. Hole as a carrier transport in
semiconductor
• A valence electron in an adjacent atom can relatively easily break
out from its covalent relationship when a bond is imperfect and a
hole results.
• A hole remains in its original location when an electron leaves a
bond to fill one. As a result, the hole really goes in the opposite
direction from the electron.
• This hole may now be filled with an electron from a different covalent
bond, in which case the hole will move one more step in the
opposite direction of the motion of the electron.
ANIL PRASAD DADI/ECE/ANITS

8. Hole as a carrier transport in
semiconductor
• The charge of a Hole is
positive.
• The movement of bound
electrons is different from the
movement of free electrons
in response of electric field,
E.
ANIL PRASAD DADI/ECE/ANITS

9. Hole as a carrier transport in
semiconductor
• Free electrons tend to move
faster as compared to bound
electrons.
• The force is same on both free
electrons and bound electrons
i.e F=qE but the rate of
movement is different.
• This difference can be captured
by assigning particle “effective
mass”. mn<mp
ANIL PRASAD DADI/ECE/ANITS

10. Extrinsic Semiconductor
• Doping: It is the Process of adding impurities into an intrinsic
semiconductor .
• Extrinsic semiconductor: Semiconductor in which impurity atoms
were added to intrinsic semiconductor to create charge carriers in
addition to intrinsic carriers generated such that the conductivity can
be made due to either electrons or holes predominantly are called
Extrinsic semiconductors.
ANIL PRASAD DADI/ECE/ANITS

11. Extrinsic Semiconductor
• n-type semiconductor: When pentavalent impurity atoms are
added to intrinsic semiconductor then n-type semiconductor is
formed.
• p-type semiconductor: When trivalent impurity atoms are added to
intrinsic semiconductor then p-type semiconductor is formed.
ANIL PRASAD DADI/ECE/ANITS

12. n-type Semiconductor
• By doping process add pentavalent atoms such as P,As etc. The
added P atoms are far away form each other because of lightly
doped. As there is no interaction among the phosphorous atoms all
the valence electrons are at the same energy level.
ANIL PRASAD DADI/ECE/ANITS

13. n-type Semiconductor
• When a pentavalent atom replaces Si
atom then it provides 4 electrons to
make covalent bond with surrounding Si
atoms and its 5th valence electron will
occupy a new energy level just below
the conduction band.
• At 1000K these impurity atoms starts
donating their 5th electron to the
conduction band of Si and are called
donar atoms.
ANIL PRASAD DADI/ECE/ANITS

14. n-type Semiconductor
• At 3000K all these impurity atoms
becomes positive charged ions after
donating their 5th valence electrons
called impurity ionization process
• At 00K no impurity atom is ionized
hence no free electrons are available in
conduction band, no EHP generation
takes place hence doped
semiconductor also acts as insulator
at T=00K
ANIL PRASAD DADI/ECE/ANITS

15. n-type Semiconductor
• In n-type semiconductor electrons are
majority charge carriers and holes are
minority charge carriers.
• n>>(ni,p)
ANIL PRASAD DADI/ECE/ANITS
n-type
EHP generation (ni)
Dopants
p-type
EHP generation (ni)

16. p-type Semiconductor
• By doping process add trivalent atoms such as
B, Al, Ga etc. The added B atoms are far away
form each other because of lightly doped. As
there is no interaction among the Boron atoms
all the valence electrons are at the same
energy level.
• When boron, a trivalent element, replaces the
silicon atom, only three of the covalent bonds
can be filled, and the empty space in the fourth
bond is referred to as a hole.
ANIL PRASAD DADI/ECE/ANITS

17. p-type Semiconductor
• When acceptor impurities are added to intrinsic
semiconductor they produce an allowable
discrete energy level which is just above VB. The
impurity level is called acceptor energy level.
• These impurities make available carriers which
are holes that can accept electrons at T=1000K.
These impurities are known as acceptor
impurities.
ANIL PRASAD DADI/ECE/ANITS

18. p-type Semiconductor
• At 3000K all these impurity atoms becomes
negative charged ions after accepting electron
form silicon atom called impurity ionization
process
• At 00K no impurity atom is ionized hence no
free holes are available in valence band, no
EHP generation takes place hence doped
semiconductor also acts as insulator at
T=00K
ANIL PRASAD DADI/ECE/ANITS

19. p-type Semiconductor
• In p-type semiconductor holes are
majority charge carriers and electrons
are minority charge carriers.
• p>>(ni,n)
ANIL PRASAD DADI/ECE/ANITS
p
EHP generation (ni)
Dopants
n
EHP generation (ni)

20. Compensated Semiconductor
• It contains both donar and acceptor impurity atoms in the same
region.
• It is called compensated semiconductor because in a p-type region
by adding ND atoms it is compensated to behave as intrinsic when
ND=NA and is compensated by adding ND>NA to behave as n-type.
ANIL PRASAD DADI/ECE/ANITS

21. References
ANIL PRASAD DADI/ECE/ANITS
• Robert L Boylestad, Electronic Devices And Circuit Theory, Prentice
Hall, seventh edition,2021
• Jacob Millman and Christos Halkias, Electronics Devices and
Circuits, Black edition, October,2017

22. Thank you
for listening
ANIL PRASAD DADI/ECE/ANITS