Hello today I am going to discuss about types of semi conductors
Semiconductors are classified into
1) Intrinsic Semiconductors (Pure Semiconductors)
2) Extrinsic Semiconductors (impure Semiconductors)
These Extrinsic Semiconductors Are again Classified into two types
1)N-Type
2)P-type
Intrinsic Semiconductors
A pure Semiconductor is called as Intrinsic Semiconductor.
In a Semiconductor at room temperature some of the valence electrons
May acquire sufficient energy to enter into the conduction band to form free electrons.
Under the influence of electric field,these electrons constitute electric current
.the missing electron leaves the empty place in the valency band that is called as Hole
*Holes also contribute electric current
In Intrinsic Semiconductors, even at room temperature ,electron Hole pairs will be created,the the conduction will takes place in the Semiconductor
Extrinsic Semiconductors
Due to poor performance of Intrinsic Semiconductor at room temperature it is not useful in electronic devices.
The Semiconductor are added with some impurities into Intrinsic Semiconductors to increase the capability of current conduction.
That Semiconductors are called as Extrinsic Semiconductors.
N-Type Semiconductors :
This type of semiconductor is obtained when a pentavalent
material like antimonty (Sb) is added to pure germanium crystal. , each
antimony atom forms covalent bonds with the surrounding four germanium atoms with the help of our of its five electrons. The fifth electron is superfluous and is loosely bound to the antimony atom. Hence, it can be easily excited from the valence band to the conduction band by the application of electric field or increase in thermal energy. Thus,
practically every antimony atom introduced
into the germanium
lattice, contributes one
conduction electron
into the germanium
lattice without creating
a positive hole.
Antimony is called donor impurity and makes the pure germanium an N-type (N for
negative) extrinsic semi-conductor. As an aid to memory, the student should associate the N in doNor
with N in the N-type material and N in Negative charge carrier.
It may be noted that by giving away its one valence electron, the donor atom becomes a positivelycharged ion. But it cannot take part in conduction because it is firmly fixed or tied into the crystal
lattice. It will be seen that apart from electrons and holes intrinsically available in germanium, the
addition of antimony greatly increases the number of conduction electrons. Hence, concentration of
electrons in the conduction band is increased and exceeds the concentration of holes in the valence
band. Because of this, Fermi level shifts upwards towards the bottom of the conduction band as
shown in Fig because the number of charge carriers has become more in conduction band
than in valence band.
In terms of energy levels, the fifth antimony electron has an energy level (called donor level) just
below the conduction band. Usually, the donor level is 0.01 eV below conduction band for germanium
and 0.054 eV for silicon
It is seen from the above description that in N-type semiconductors, electrons are the majority
carriers while holes constitute the minority carriers. Hence, N-type semiconductor conducts principally by electrons in the nearly empty conduction band and the process is called ‘excess’ conduction.
Another point worth noting is that even though N-type semiconductor has excess of electrons,
still it is electrically neutral. It is so because by the addition of donor impurity, number of electrons available for conduction purposes becomes more than the number of holes available intrinsically. But the total charge of the semiconductor does not change because the donor impurity brings in as much negative charge (by way of electrons) as positive charge (by way of protons in its nucleus)
P-Type Semiconductors :
This type of semiconductor is obtained when traces of a
trivalent like boron (B) are added to a pure germanium crystal.
In this case, the three valence electrons of boron atom form covalent bonds with four surrounding
germanium atoms but one bond is left incomplete and gives rise to a hole as shown in Fig. 51.25 (a).
Thus, boron which is called an acceptor impurity causes as many positive holes in a germanium
crystal as there are boron atoms thereby producing a P-type (P for positive) extrinsic semiconductor.
As an aid to memory, the student should associate the P in accePtor with P in P-type material and P
with Positive charge carrier.
In this type of semiconductor, conduction is by the movement of holes in the valence band.
Accordingly, holes form the majority carriers whereas electrons constitute minority carriers. The
process of conduction is called ‘deficit’ conduction.
Semiconductors are classified into
1) Intrinsic Semiconductors (Pure Semiconductors)
2) Extrinsic Semiconductors (impure Semiconductors)
These Extrinsic Semiconductors Are again Classified into two types
1)N-Type
2)P-type
Intrinsic Semiconductors
A pure Semiconductor is called as Intrinsic Semiconductor.
In a Semiconductor at room temperature some of the valence electrons
May acquire sufficient energy to enter into the conduction band to form free electrons.
Under the influence of electric field,these electrons constitute electric current
.the missing electron leaves the empty place in the valency band that is called as Hole
*Holes also contribute electric current
In Intrinsic Semiconductors, even at room temperature ,electron Hole pairs will be created,the the conduction will takes place in the Semiconductor
Extrinsic Semiconductors
Due to poor performance of Intrinsic Semiconductor at room temperature it is not useful in electronic devices.
The Semiconductor are added with some impurities into Intrinsic Semiconductors to increase the capability of current conduction.
That Semiconductors are called as Extrinsic Semiconductors.
N-Type Semiconductors :
This type of semiconductor is obtained when a pentavalent
material like antimonty (Sb) is added to pure germanium crystal. , each
antimony atom forms covalent bonds with the surrounding four germanium atoms with the help of our of its five electrons. The fifth electron is superfluous and is loosely bound to the antimony atom. Hence, it can be easily excited from the valence band to the conduction band by the application of electric field or increase in thermal energy. Thus,
practically every antimony atom introduced
into the germanium
lattice, contributes one
conduction electron
into the germanium
lattice without creating
a positive hole.
Antimony is called donor impurity and makes the pure germanium an N-type (N for
negative) extrinsic semi-conductor. As an aid to memory, the student should associate the N in doNor
with N in the N-type material and N in Negative charge carrier.
It may be noted that by giving away its one valence electron, the donor atom becomes a positivelycharged ion. But it cannot take part in conduction because it is firmly fixed or tied into the crystal
lattice. It will be seen that apart from electrons and holes intrinsically available in germanium, the
addition of antimony greatly increases the number of conduction electrons. Hence, concentration of
electrons in the conduction band is increased and exceeds the concentration of holes in the valence
band. Because of this, Fermi level shifts upwards towards the bottom of the conduction band as
shown in Fig because the number of charge carriers has become more in conduction band
than in valence band.
In terms of energy levels, the fifth antimony electron has an energy level (called donor level) just
below the conduction band. Usually, the donor level is 0.01 eV below conduction band for germanium
and 0.054 eV for silicon
It is seen from the above description that in N-type semiconductors, electrons are the majority
carriers while holes constitute the minority carriers. Hence, N-type semiconductor conducts principally by electrons in the nearly empty conduction band and the process is called ‘excess’ conduction.
Another point worth noting is that even though N-type semiconductor has excess of electrons,
still it is electrically neutral. It is so because by the addition of donor impurity, number of electrons available for conduction purposes becomes more than the number of holes available intrinsically. But the total charge of the semiconductor does not change because the donor impurity brings in as much negative charge (by way of electrons) as positive charge (by way of protons in its nucleus)
P-Type Semiconductors :
This type of semiconductor is obtained when traces of a
trivalent like boron (B) are added to a pure germanium crystal.
In this case, the three valence electrons of boron atom form covalent bonds with four surrounding
germanium atoms but one bond is left incomplete and gives rise to a hole as shown in Fig. 51.25 (a).
Thus, boron which is called an acceptor impurity causes as many positive holes in a germanium
crystal as there are boron atoms thereby producing a P-type (P for positive) extrinsic semiconductor.
As an aid to memory, the student should associate the P in accePtor with P in P-type material and P
with Positive charge carrier.
In this type of semiconductor, conduction is by the movement of holes in the valence band.
Accordingly, holes form the majority carriers whereas electrons constitute minority carriers. The
process of conduction is called ‘deficit’ conduction.
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