Lecture Electronic Circuits. www.fida.com.bd

1. EEE-201
Lecture 2
www.fida.com.bd

2. EXTRINSIC MATERIAL
• The characteristic of semiconductor can
be altered by adding impurity through
doping process (extrinsic material)
• Two type:
– N-type
– P-type
www.fida.com.bd

3. N-TYPE
• N-type is created by
introducing impurity elements
that have five valence
electrons (pentavalent) –
antimony, arsenic, phosphorus
• Note that four covalent bonds
are still present, however there
is additional fifth electron due
to impurity atom
• The remaining electron is free
to move within the newly
formed n-type material
• Diffused impurities with five
Figure 1.9 Antimony
valence electrons are called impurity in n-type material
donor atoms www.fida.com.bd

4. P-TYPE
• P-type is created by doping
with impurity atoms having
three valence electrons –
boron gallium, indium
• Note that there are
insufficient number of
electrons to complete
covalent bonds resulting a
hole
• This hole is ready to accept
a free electron
• The diffused impurities with
three valence electrons are Figure 1.11 Boron impurity
called acceptor atoms. in p-type material
www.fida.com.bd

5. Electron versus Hole Flow
www.fida.com.bd

6. Majority and Minority Carriers
• In an n-type material - electron is called majority
carrier and hole the minority carrier
• In a p-type material – hole is majority carrier and
electron is the minority carrier
www.fida.com.bd

7. Semiconductor Diode
• Diode is formed by bringing these two material together p- and
n-type
• Electrons and holes at joined region will combine, resulting in a
lack of carriers in the region near the junction (depletion region)
www.fida.com.bd

8. • Since the diode is two-terminal device,
the application of a voltage across its
terminals leaves three possibilities:
– No bias (VD = 0V)
– Foreard bias (VD > 0V)
– Reversed bias (VD < 0V)
• Each condition will result in a response
www.fida.com.bd

9. No Applied Bias (VD = 0V)
• Under no-bias conditions, any minority carries (holes) in the n-type
material find themselves within the depletion region will pass directly
into p-type material
• Majority carriers (electrons) of n-type material must overcome the
attractive forces of the layer of positive ions in n-type material and the
shield of negative ions in p-type material to migrate into the area
beyond the depletion region of p-type material.
• In the absence of an applied bias voltage, the net flow of charge in
any one direction for semiconductor diode is zero
www.fida.com.bd

10. Figure 1.14 p-n junction with no external bias
www.fida.com.bd

11. www.fida.com.bd

12. Reverse-Bias Condition (VD < 0V)
• The number of uncovered positive ions in the depletion
region of n-type will increase due to large number of free
electrons drawn to the positive potential
• The number of uncovered negative ions will increase in p-
type resulting widening of depletion region
• This region established great barrier for the majority
carriers to overcome – resulting Imajority = 0
• The number pf minority carriers find themselves entering
the depletion region will not change resulting in minority-
carrier flow vectors of the same magnitude
• The current exists under reverse-bias conditions is called
the reverse saturation current and represented by Is
• Therefore, ID= -Is www.fida.com.bd

13. Figure 1-16 Reverse-biased p-n junction
www.fida.com.bd

14. www.fida.com.bd

15. Forward-Bias Condition (VD = 0V)
• A semiconductor diode is forward-biased when the
association p-type and positive and n-type and negative
has been established
• The application of forward-bias potential will pressure the
electrons in n-type and hole in p-type to recombine with
ions near the boundary and reduce the width of depletion
region
• The resulting minority-carrier flow of electrons from p-
type to n-type has not changed in magnitude, but the
reduction in width of depletion region has resulted in a
heavy majority flow across the junction
www.fida.com.bd

16. Figure 1.18 Forward-biased p-n junction
www.fida.com.bd

17. For Forward-bias and Reverse-bias
(1.4)
www.fida.com.bd

18. Figure 1.19 Silicon semiconductor diode characteristics
www.fida.com.bd

19. www.fida.com.bd

20. www.fida.com.bd