This ppt is about semiconductor diodes.You can get every basic information about PN junction diode and its working and some more information about the semiconductors.
2. OBJECTIVE
Energy band and energy band gap
Classification of materials on the basis of
energy band gap
What is Semiconductor
Types of semiconductor
Extrinsic semiconductor
Semiconductor junction
Semiconductor device (P-N DIODE)
Applications of diode
3. DIFFERENCE BETWEEN
CONDUCTORS,INSULATORS,SEMICONDUCTORS
Energy band & energy band gap:-
Each isolated atom has a discrete
energy level. But in general isolated atoms are not exist .they
exist in the form of crystal. In that crystal there are nearby atoms
,which also have an energy level nearly equal to the previous
energy level.
so these “closely spaced energy levels form a band
of energy” called energy band.
valance band is located blow the conduction band eperated from
it by a energy band gap.
• In conductors C.B. and V.B. are overlapped
• In insulators energy band gap is 6eV
• In semiconductors energy band gap is 1eV
5. SEMICONDUCTOR
Semiconductor are those materials which
behaves like insulators at 0 degree Celsius
and like conductor at room temperature.
They have properties between conductors
and insulators.
6. TYPES OF SEMICONDUCTOR
Intrinsic semiconductors:-
Intrinsic semiconductors are
pure semiconductors, no impurities are added
in these conductors.
So the no. of free electrons and holes are
equal . Conductivity of these semiconductors is
low because of electrons are in perfect
covalent bonding.
Extrinsic semiconductors
7. INTRINSIC (PURE) SILICON
At 0 Kelvin Silicon density is
5*10²³particles/cm³
Silicon has 4 valence electrons, it
covalently bonds with four adjacent
atoms in the crystal lattice
Higher temperatures create free
charge carriers.
A “hole” is created in the absence of
an electron.
At 23C there are 10¹º particles/cm³ of
free carriers
8. EXTRINSIC SEMICONDUCTORS
An extrinsic semiconductor is a semiconductor that
has been doped, that is, into which a doping agent has
been introduced, giving it different electrical properties
than theintrinsic (pure) semiconductor.
9. DOPING INVOLVES ADDING DOPANT ATOMS TO AN INTRINSIC
SEMICONDUCTOR, WHICH CHANGES THE ELECTRON AND HOLE CARRIER
CONCENTRATIONS OF THE SEMICONDUCTOR AT THERMAL EQUILIBRIUM.
DOMINANT CARRIER CONCENTRATIONS IN AN EXTRINSIC SEMICONDUCTOR
CLASSIFY IT AS EITHER AN N-TYPE OR P-TYPE SEMICONDUCTOR. THE
ELECTRICAL PROPERTIES OF EXTRINSIC SEMICONDUCTORS MAKE THEM
ESSENTIAL COMPONENTS OF MANY ELECTRONIC DEVICES.
11. P-TYPE N-TYPE
When a doped
semiconductor
contains excess holes
it is called P-type
semiconductor.
Doping is
trivalent,B,Ga,In,Al
When a dped
semiconductor contains
excess electrons it is
called N-type
semiconductor.
Doping is
pentavalent,As,Bi,Sb,P
12. DOPING
The N in N-type stands for negative.
A column V ion is inserted.
The extra valence electron is free to
move about the lattice
There are two types of doping
N-type and P-type.
The P in P-type stands for positive.
A column III ion is inserted.
Electrons from the surrounding
Silicon move to fill the “hole.”
13. CRYSTALLINE NATURE OF SILICON
Silicon as utilized in integrated circuits is
crystalline in nature
As with all crystalline material, silicon
consists of a repeating basic unit structure
called a unit cell
For silicon, the unit cell consists of an atom
surrounded by four equidistant nearest
neighbors which lie at the corners of the
tetrahedron
14.
15. P-N JUNCTION
Also known as a diode
One of the basics of semiconductor
technology -
Created by placing n-type and p-type
material in close contact
Diffusion - mobile charges (holes) in p-
type combine with mobile charges
(electrons) in n-type
16. P-N JUNCTION
Region of charges left behind (dopants
fixed in crystal lattice)
Group III in p-type (one less proton than Si-
negative charge)
Group IV in n-type (one more proton than
Si - positive charge)
Region is totally depleted of mobile
charges - “depletion region”
Electric field forms due to fixed charges in
the depletion region
Depletion region has high resistance due
to lack of mobile charges
18. THE JUNCTION
The “potential” or voltage across the silicon
changes in the depletion region and goes from
+ in the n region to – in the p region
19. BIASING THE P-N DIODE
Forward Bias
Applies - voltage
to the n region and
+ voltage to the p
region
CURRENT!
Reverse Bias
Applies + voltage
to n region and –
voltage to p region
NO CURRENT
THINK OF THE DIODE
AS A SWITCH
20. P-N JUNCTION – REVERSE BIAS
positive voltage placed on n-type
material
electrons in n-type move closer to
positive terminal, holes in p-type move
closer to negative terminal
width of depletion region increases
allowed current is essentially zero
(small “drift” current)
21. P-N JUNCTION – FORWARD BIAS
positive voltage placed on p-type material
holes in p-type move away from positive
terminal, electrons in n-type move further
from negative terminal
depletion region becomes smaller -
resistance of device decreases
voltage increased until critical voltage is
reached, depletion region disappears,
current can flow freely
22. P-N JUNCTION - V-I CHARACTERISTICS
Voltage-Current relationship for a p-n junction (diode)
24. I I
qV
kT
where
I diode current with reverse bias
q coulomb the electronic ch e
k
eV
K
Boltzmann s cons t
0
0
19
5
1
1602 10
8 62 10
exp ,
. , arg
. , ' tan
THE IDEAL DIODE EQUATION
25. SEMICONDUCTOR DIODE - OPENED REGION
The p-side is the cathode, the n-side is the anode
The dropped voltage, VD is measured from the
cathode to the anode
Opened: VD VF:
VD = VF
ID = circuit limited, in our model the VD cannot exceed
VF
26. SEMICONDUCTOR DIODE - CUT-OFF REGION
Cut-off: 0 < VD < VF:
ID 0 mA
SEMICONDUCTOR DIODE - CLOSED REGION
Closed: VF < VD 0:
VD is determined by the circuit, ID
= 0 mA
Typical values of VF: 0.5 ¸ 0.7 V
27. ZENER EFFECT
Zener break down: VD <= VZ:
VD = VZ, ID is determined by the circuit.
In case of standard diode the typical values of the
break down voltage VZ of the Zener effect -20 ... -
100 V
Zener diode
Utilization of the Zener effect
Typical break down values of VZ : -4.5 ... -15 V