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pn JUNCTIONauthor: Teacher Engineer NICA MADALINA
“Costin Nenitescu” Highschool for Chemistry, Romania
Translated by Catalina Rinescu and Adriana Gaspar, english teachers
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Nonpolarized pn junctionp n
Impurities atoms
Minority carriers
Majority carriers
npRegion
voids electrons
electrons voidsReceiver atoms Donor atoms
LEGENDUM
void
electron
Donor atom positively ionized
Receiver atom negatively ionized
Power DiagramConductive band
Valence band
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Nonpolarized pn junctionp n
Power Diagram
Conductive band
Valence band
Impurities atoms
Minority carriers
Majority carriers
npRegion
voids electrons
electrons voidsReceiver atoms Donor atoms
LEGENDUM
void
electron
Ionized donor atom
Ionized receiver atom
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Nonpolarized pn junction
p n
Impurities atoms
Minority carriers
Majority carriers
npRegion
voids electrons
electrons voidsReceiver atoms Donor atoms
LEGENDUM
void
electron
Ionized donor atom
Ionized receiver atom
Power Diagram
Conductive band
Valence band
Ec
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WORK SHEET
Polarized pn junction
Polarized pn junction ..............................
Polarized pn junction ..............................
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Polarized pn junction
p nelectrod
p n
+ - +-
- ++ -
direct polarization reverse polarization
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a) Direct polarized pn junction
It is obtained by connecting:- the plus clamp of the source to region p - the minus clamp of the source to region n
p n
+ -
+ -
U
Ec
E
This has the direction reverse to the contact field Ec, which is oriented from region n (positive space electric charges) to region p (negative space electric charges).
The applied tension creates the electrical field E, oriented from region p (+ of the source) to region n (– of the source).
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a) Directly polarized pn junctionAs a result of the fact that the applied field of E intensity has a value bigger than the contact field of Ec intensity, the movement of electric charge carriers is determined by a resulting field, which has the intensity, in absolute value, equal to the difference between the intensities of the two fields: Eresulting=E-Ec
p n
+ -
+ -
U
The result is:- the voids in region p (attracted to the – of the source) move from region p to region n
- the electrons in region n (attracted to the + of the source) move from region n to region p
Ec
E
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a) Directly polarized pn junction
p n
Power diagram
-+
-+
Ec
E
Eresulting=E-Ec
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a) Directly polarized pn junction
p n
+ -
+ -
U
Idirect
Through the directly polarized pn junction it appears an electric power which has the direction from region p to region n and which is called direct power. I direct
Ec
E
Eresulting=E-Ec
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b) Reverse polarized pn junction
p n
- +
- +
U
Ec
The applied tension creates an electric field E, oriented from region n (+ of source) to region p (–of source)
E
This has the same direction as the contact field Ec, fortifying its action.
It is obtained by connecting:- the minus clamp of the source to region p - the plus clamp of the source to region n
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p n
- +
- +
U
b) Reverse polarized pn junction
Ec
E
The result is:-the voids in region p, attracted to the –of source, removes from the junction- the electrons in region n, attracted to the+ of source, removes from the junction
Both on the left and on the right sides of the junction it will appear a region low in electric charge carriers, which is called blocking layer.
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a) Reverse polarized pn junction
p n
Power diagram
+-
+-
Ec
E
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p n
- +
- +
U
Ec
E
b) Reverse polarized pn junction
Iinvers ~ 0
Majority carriers (electrons) in region p, attracted to +of source, move to region n
In the circuit it appears a very low electric power because of minority carriers, called curent reverse, which is directed from n to p.
Minority carriers (voids) in region n, attracted to –of source, move to region p
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a) Reverse polarized pn junction
p n
Power diagram
Ec
+-
+-
E
Ireverse ~ 0
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Conclusion:
Fig. II.aDirect polarization
p n
- +
- +
U
Ec
E
Idirect
p n
+ -
+ -
U
Ec
E
Fig. II b Reverse polarization
Ireverse~0
The pn junction works as an electrical contact with no mecanical elements.
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n p