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9 | 3339-3342 | 4 EXTRINSIC SEMICONDUCTOR
The conductivity of an intrinsic semiconductor depends on its
temperature, but at room temperature its conductivity is very low As
such, no important electronic devices can be developed using these
semiconductors Hence there is a necessity of improving their
conductivity This can be done by making use of impurities |
9 | 3340-3343 | As
such, no important electronic devices can be developed using these
semiconductors Hence there is a necessity of improving their
conductivity This can be done by making use of impurities When a small amount, say, a few parts per million (ppm), of a suitable
impurity is added to the pure semiconductor, the conductivity of the
semiconductor is increased manifold |
9 | 3341-3344 | Hence there is a necessity of improving their
conductivity This can be done by making use of impurities When a small amount, say, a few parts per million (ppm), of a suitable
impurity is added to the pure semiconductor, the conductivity of the
semiconductor is increased manifold Such materials are known as
extrinsic semiconductors or impurity semiconductors |
9 | 3342-3345 | This can be done by making use of impurities When a small amount, say, a few parts per million (ppm), of a suitable
impurity is added to the pure semiconductor, the conductivity of the
semiconductor is increased manifold Such materials are known as
extrinsic semiconductors or impurity semiconductors The deliberate
addition of a desirable impurity is called doping and the impurity atoms
are called dopants |
9 | 3343-3346 | When a small amount, say, a few parts per million (ppm), of a suitable
impurity is added to the pure semiconductor, the conductivity of the
semiconductor is increased manifold Such materials are known as
extrinsic semiconductors or impurity semiconductors The deliberate
addition of a desirable impurity is called doping and the impurity atoms
are called dopants Such a material is also called a doped semiconductor |
9 | 3344-3347 | Such materials are known as
extrinsic semiconductors or impurity semiconductors The deliberate
addition of a desirable impurity is called doping and the impurity atoms
are called dopants Such a material is also called a doped semiconductor The dopant has to be such that it does not distort the original pure
semiconductor lattice |
9 | 3345-3348 | The deliberate
addition of a desirable impurity is called doping and the impurity atoms
are called dopants Such a material is also called a doped semiconductor The dopant has to be such that it does not distort the original pure
semiconductor lattice It occupies only a very few of the original
semiconductor atom sites in the crystal |
9 | 3346-3349 | Such a material is also called a doped semiconductor The dopant has to be such that it does not distort the original pure
semiconductor lattice It occupies only a very few of the original
semiconductor atom sites in the crystal A necessary condition to attain
this is that the sizes of the dopant and the semiconductor atoms should
be nearly the same |
9 | 3347-3350 | The dopant has to be such that it does not distort the original pure
semiconductor lattice It occupies only a very few of the original
semiconductor atom sites in the crystal A necessary condition to attain
this is that the sizes of the dopant and the semiconductor atoms should
be nearly the same There are two types of dopants used in doping the tetravalent Si
or Ge:
(i)
Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous
(P), etc |
9 | 3348-3351 | It occupies only a very few of the original
semiconductor atom sites in the crystal A necessary condition to attain
this is that the sizes of the dopant and the semiconductor atoms should
be nearly the same There are two types of dopants used in doping the tetravalent Si
or Ge:
(i)
Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous
(P), etc FIGURE 14 |
9 | 3349-3352 | A necessary condition to attain
this is that the sizes of the dopant and the semiconductor atoms should
be nearly the same There are two types of dopants used in doping the tetravalent Si
or Ge:
(i)
Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous
(P), etc FIGURE 14 6 (a) An intrinsic semiconductor at T = 0 K
behaves like insulator |
9 | 3350-3353 | There are two types of dopants used in doping the tetravalent Si
or Ge:
(i)
Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous
(P), etc FIGURE 14 6 (a) An intrinsic semiconductor at T = 0 K
behaves like insulator (b) At T > 0 K, four thermally generated
electron-hole pairs |
9 | 3351-3354 | FIGURE 14 6 (a) An intrinsic semiconductor at T = 0 K
behaves like insulator (b) At T > 0 K, four thermally generated
electron-hole pairs The filled circles ( ) represent electrons
and empty circles ( ) represent holes |
9 | 3352-3355 | 6 (a) An intrinsic semiconductor at T = 0 K
behaves like insulator (b) At T > 0 K, four thermally generated
electron-hole pairs The filled circles ( ) represent electrons
and empty circles ( ) represent holes Rationalised 2023-24
Physics
330
(ii) Trivalent (valency 3); like Indium (In),
Boron (B), Aluminium (Al), etc |
9 | 3353-3356 | (b) At T > 0 K, four thermally generated
electron-hole pairs The filled circles ( ) represent electrons
and empty circles ( ) represent holes Rationalised 2023-24
Physics
330
(ii) Trivalent (valency 3); like Indium (In),
Boron (B), Aluminium (Al), etc We shall now discuss how the doping
changes the number of charge carriers (and
hence the conductivity) of semiconductors |
9 | 3354-3357 | The filled circles ( ) represent electrons
and empty circles ( ) represent holes Rationalised 2023-24
Physics
330
(ii) Trivalent (valency 3); like Indium (In),
Boron (B), Aluminium (Al), etc We shall now discuss how the doping
changes the number of charge carriers (and
hence the conductivity) of semiconductors Si or Ge belongs to the fourth group in the
Periodic table and, therefore, we choose the
dopant element from nearby fifth or third
group, expecting and taking care that the
size of the dopant atom is nearly the same as
that of Si or Ge |
9 | 3355-3358 | Rationalised 2023-24
Physics
330
(ii) Trivalent (valency 3); like Indium (In),
Boron (B), Aluminium (Al), etc We shall now discuss how the doping
changes the number of charge carriers (and
hence the conductivity) of semiconductors Si or Ge belongs to the fourth group in the
Periodic table and, therefore, we choose the
dopant element from nearby fifth or third
group, expecting and taking care that the
size of the dopant atom is nearly the same as
that of Si or Ge Interestingly, the pentavalent
and trivalent dopants in Si or Ge give two
entirely different types of semiconductors as
discussed below |
9 | 3356-3359 | We shall now discuss how the doping
changes the number of charge carriers (and
hence the conductivity) of semiconductors Si or Ge belongs to the fourth group in the
Periodic table and, therefore, we choose the
dopant element from nearby fifth or third
group, expecting and taking care that the
size of the dopant atom is nearly the same as
that of Si or Ge Interestingly, the pentavalent
and trivalent dopants in Si or Ge give two
entirely different types of semiconductors as
discussed below (i) n-type semiconductor
Suppose we dope Si or Ge with a pentavalent
element as shown in Fig |
9 | 3357-3360 | Si or Ge belongs to the fourth group in the
Periodic table and, therefore, we choose the
dopant element from nearby fifth or third
group, expecting and taking care that the
size of the dopant atom is nearly the same as
that of Si or Ge Interestingly, the pentavalent
and trivalent dopants in Si or Ge give two
entirely different types of semiconductors as
discussed below (i) n-type semiconductor
Suppose we dope Si or Ge with a pentavalent
element as shown in Fig 14 |
9 | 3358-3361 | Interestingly, the pentavalent
and trivalent dopants in Si or Ge give two
entirely different types of semiconductors as
discussed below (i) n-type semiconductor
Suppose we dope Si or Ge with a pentavalent
element as shown in Fig 14 7 |
9 | 3359-3362 | (i) n-type semiconductor
Suppose we dope Si or Ge with a pentavalent
element as shown in Fig 14 7 When an atom
of +5 valency element occupies the position
of an atom in the crystal lattice of Si, four of
its electrons bond with the four silicon
neighbours while the fifth remains very
weakly bound to its parent atom |
9 | 3360-3363 | 14 7 When an atom
of +5 valency element occupies the position
of an atom in the crystal lattice of Si, four of
its electrons bond with the four silicon
neighbours while the fifth remains very
weakly bound to its parent atom This is
because the four electrons participating in
bonding are seen as part of the effective core
of the atom by the fifth electron |
9 | 3361-3364 | 7 When an atom
of +5 valency element occupies the position
of an atom in the crystal lattice of Si, four of
its electrons bond with the four silicon
neighbours while the fifth remains very
weakly bound to its parent atom This is
because the four electrons participating in
bonding are seen as part of the effective core
of the atom by the fifth electron As a result
the ionisation energy required to set this
electron free is very small and even at room
temperature it will be free to move in the
lattice of the semiconductor |
9 | 3362-3365 | When an atom
of +5 valency element occupies the position
of an atom in the crystal lattice of Si, four of
its electrons bond with the four silicon
neighbours while the fifth remains very
weakly bound to its parent atom This is
because the four electrons participating in
bonding are seen as part of the effective core
of the atom by the fifth electron As a result
the ionisation energy required to set this
electron free is very small and even at room
temperature it will be free to move in the
lattice of the semiconductor For example, the
energy required is ~ 0 |
9 | 3363-3366 | This is
because the four electrons participating in
bonding are seen as part of the effective core
of the atom by the fifth electron As a result
the ionisation energy required to set this
electron free is very small and even at room
temperature it will be free to move in the
lattice of the semiconductor For example, the
energy required is ~ 0 01 eV for germanium,
and 0 |
9 | 3364-3367 | As a result
the ionisation energy required to set this
electron free is very small and even at room
temperature it will be free to move in the
lattice of the semiconductor For example, the
energy required is ~ 0 01 eV for germanium,
and 0 05 eV for silicon, to separate this
electron from its atom |
9 | 3365-3368 | For example, the
energy required is ~ 0 01 eV for germanium,
and 0 05 eV for silicon, to separate this
electron from its atom This is in contrast to the energy required to jump
the forbidden band (about 0 |
9 | 3366-3369 | 01 eV for germanium,
and 0 05 eV for silicon, to separate this
electron from its atom This is in contrast to the energy required to jump
the forbidden band (about 0 72 eV for germanium and about 1 |
9 | 3367-3370 | 05 eV for silicon, to separate this
electron from its atom This is in contrast to the energy required to jump
the forbidden band (about 0 72 eV for germanium and about 1 1 eV for
silicon) at room temperature in the intrinsic semiconductor |
9 | 3368-3371 | This is in contrast to the energy required to jump
the forbidden band (about 0 72 eV for germanium and about 1 1 eV for
silicon) at room temperature in the intrinsic semiconductor Thus, the
pentavalent dopant is donating one extra electron for conduction and
hence is known as donor impurity |
9 | 3369-3372 | 72 eV for germanium and about 1 1 eV for
silicon) at room temperature in the intrinsic semiconductor Thus, the
pentavalent dopant is donating one extra electron for conduction and
hence is known as donor impurity The number of electrons made
available for conduction by dopant atoms depends strongly upon the
doping level and is independent of any increase in ambient temperature |
9 | 3370-3373 | 1 eV for
silicon) at room temperature in the intrinsic semiconductor Thus, the
pentavalent dopant is donating one extra electron for conduction and
hence is known as donor impurity The number of electrons made
available for conduction by dopant atoms depends strongly upon the
doping level and is independent of any increase in ambient temperature On the other hand, the number of free electrons (with an equal number
of holes) generated by Si atoms, increases weakly with temperature |
9 | 3371-3374 | Thus, the
pentavalent dopant is donating one extra electron for conduction and
hence is known as donor impurity The number of electrons made
available for conduction by dopant atoms depends strongly upon the
doping level and is independent of any increase in ambient temperature On the other hand, the number of free electrons (with an equal number
of holes) generated by Si atoms, increases weakly with temperature In a doped semiconductor the total number of conduction electrons
ne is due to the electrons contributed by donors and those generated
intrinsically, while the total number of holes nh is only due to the holes
from the intrinsic source |
9 | 3372-3375 | The number of electrons made
available for conduction by dopant atoms depends strongly upon the
doping level and is independent of any increase in ambient temperature On the other hand, the number of free electrons (with an equal number
of holes) generated by Si atoms, increases weakly with temperature In a doped semiconductor the total number of conduction electrons
ne is due to the electrons contributed by donors and those generated
intrinsically, while the total number of holes nh is only due to the holes
from the intrinsic source But the rate of recombination of holes would
increase due to the increase in the number of electrons |
9 | 3373-3376 | On the other hand, the number of free electrons (with an equal number
of holes) generated by Si atoms, increases weakly with temperature In a doped semiconductor the total number of conduction electrons
ne is due to the electrons contributed by donors and those generated
intrinsically, while the total number of holes nh is only due to the holes
from the intrinsic source But the rate of recombination of holes would
increase due to the increase in the number of electrons As a result, the
number of holes would get reduced further |
9 | 3374-3377 | In a doped semiconductor the total number of conduction electrons
ne is due to the electrons contributed by donors and those generated
intrinsically, while the total number of holes nh is only due to the holes
from the intrinsic source But the rate of recombination of holes would
increase due to the increase in the number of electrons As a result, the
number of holes would get reduced further Thus, with proper level of doping the number of conduction electrons
can be made much larger than the number of holes |
9 | 3375-3378 | But the rate of recombination of holes would
increase due to the increase in the number of electrons As a result, the
number of holes would get reduced further Thus, with proper level of doping the number of conduction electrons
can be made much larger than the number of holes Hence in an extrinsic
FIGURE 14 |
9 | 3376-3379 | As a result, the
number of holes would get reduced further Thus, with proper level of doping the number of conduction electrons
can be made much larger than the number of holes Hence in an extrinsic
FIGURE 14 7 (a) Pentavalent donor atom (As, Sb,
P, etc |
9 | 3377-3380 | Thus, with proper level of doping the number of conduction electrons
can be made much larger than the number of holes Hence in an extrinsic
FIGURE 14 7 (a) Pentavalent donor atom (As, Sb,
P, etc ) doped for tetravalent Si or Ge giving n-
type semiconductor, and (b) Commonly used
schematic representation of n-type material
which shows only the fixed cores of the
substituent donors with one additional effective
positive charge and its associated extra electron |
9 | 3378-3381 | Hence in an extrinsic
FIGURE 14 7 (a) Pentavalent donor atom (As, Sb,
P, etc ) doped for tetravalent Si or Ge giving n-
type semiconductor, and (b) Commonly used
schematic representation of n-type material
which shows only the fixed cores of the
substituent donors with one additional effective
positive charge and its associated extra electron Rationalised 2023-24
331
Semiconductor Electronics:
Materials, Devices and
Simple Circuits
semiconductor doped with pentavalent impurity, electrons
become the majority carriers and holes the minority carriers |
9 | 3379-3382 | 7 (a) Pentavalent donor atom (As, Sb,
P, etc ) doped for tetravalent Si or Ge giving n-
type semiconductor, and (b) Commonly used
schematic representation of n-type material
which shows only the fixed cores of the
substituent donors with one additional effective
positive charge and its associated extra electron Rationalised 2023-24
331
Semiconductor Electronics:
Materials, Devices and
Simple Circuits
semiconductor doped with pentavalent impurity, electrons
become the majority carriers and holes the minority carriers These semiconductors are, therefore, known as n-type
semiconductors |
9 | 3380-3383 | ) doped for tetravalent Si or Ge giving n-
type semiconductor, and (b) Commonly used
schematic representation of n-type material
which shows only the fixed cores of the
substituent donors with one additional effective
positive charge and its associated extra electron Rationalised 2023-24
331
Semiconductor Electronics:
Materials, Devices and
Simple Circuits
semiconductor doped with pentavalent impurity, electrons
become the majority carriers and holes the minority carriers These semiconductors are, therefore, known as n-type
semiconductors For n-type semiconductors, we have,
ne >> nh
(14 |
9 | 3381-3384 | Rationalised 2023-24
331
Semiconductor Electronics:
Materials, Devices and
Simple Circuits
semiconductor doped with pentavalent impurity, electrons
become the majority carriers and holes the minority carriers These semiconductors are, therefore, known as n-type
semiconductors For n-type semiconductors, we have,
ne >> nh
(14 3)
(ii) p-type semiconductor
This is obtained when Si or Ge is doped with a trivalent impurity
like Al, B, In, etc |
9 | 3382-3385 | These semiconductors are, therefore, known as n-type
semiconductors For n-type semiconductors, we have,
ne >> nh
(14 3)
(ii) p-type semiconductor
This is obtained when Si or Ge is doped with a trivalent impurity
like Al, B, In, etc The dopant has one valence electron less than
Si or Ge and, therefore, this atom can form covalent bonds with
neighbouring three Si atoms but does not have any electron to
offer to the fourth Si atom |
9 | 3383-3386 | For n-type semiconductors, we have,
ne >> nh
(14 3)
(ii) p-type semiconductor
This is obtained when Si or Ge is doped with a trivalent impurity
like Al, B, In, etc The dopant has one valence electron less than
Si or Ge and, therefore, this atom can form covalent bonds with
neighbouring three Si atoms but does not have any electron to
offer to the fourth Si atom So the bond between the fourth
neighbour and the trivalent atom has a vacancy or hole as
shown in Fig |
9 | 3384-3387 | 3)
(ii) p-type semiconductor
This is obtained when Si or Ge is doped with a trivalent impurity
like Al, B, In, etc The dopant has one valence electron less than
Si or Ge and, therefore, this atom can form covalent bonds with
neighbouring three Si atoms but does not have any electron to
offer to the fourth Si atom So the bond between the fourth
neighbour and the trivalent atom has a vacancy or hole as
shown in Fig 14 |
9 | 3385-3388 | The dopant has one valence electron less than
Si or Ge and, therefore, this atom can form covalent bonds with
neighbouring three Si atoms but does not have any electron to
offer to the fourth Si atom So the bond between the fourth
neighbour and the trivalent atom has a vacancy or hole as
shown in Fig 14 8 |
9 | 3386-3389 | So the bond between the fourth
neighbour and the trivalent atom has a vacancy or hole as
shown in Fig 14 8 Since the neighbouring Si atom in the lattice
wants an electron in place of a hole, an electron in the outer
orbit of an atom in the neighbourhood may jump to fill this
vacancy, leaving a vacancy or hole at its own site |
9 | 3387-3390 | 14 8 Since the neighbouring Si atom in the lattice
wants an electron in place of a hole, an electron in the outer
orbit of an atom in the neighbourhood may jump to fill this
vacancy, leaving a vacancy or hole at its own site Thus the hole
is available for conduction |
9 | 3388-3391 | 8 Since the neighbouring Si atom in the lattice
wants an electron in place of a hole, an electron in the outer
orbit of an atom in the neighbourhood may jump to fill this
vacancy, leaving a vacancy or hole at its own site Thus the hole
is available for conduction Note that the trivalent foreign atom
becomes effectively negatively charged when it shares fourth
electron with neighbouring Si atom |
9 | 3389-3392 | Since the neighbouring Si atom in the lattice
wants an electron in place of a hole, an electron in the outer
orbit of an atom in the neighbourhood may jump to fill this
vacancy, leaving a vacancy or hole at its own site Thus the hole
is available for conduction Note that the trivalent foreign atom
becomes effectively negatively charged when it shares fourth
electron with neighbouring Si atom Therefore, the dopant atom
of p-type material can be treated as core of one negative charge
along with its associated hole as shown in Fig |
9 | 3390-3393 | Thus the hole
is available for conduction Note that the trivalent foreign atom
becomes effectively negatively charged when it shares fourth
electron with neighbouring Si atom Therefore, the dopant atom
of p-type material can be treated as core of one negative charge
along with its associated hole as shown in Fig 14 |
9 | 3391-3394 | Note that the trivalent foreign atom
becomes effectively negatively charged when it shares fourth
electron with neighbouring Si atom Therefore, the dopant atom
of p-type material can be treated as core of one negative charge
along with its associated hole as shown in Fig 14 8(b) |
9 | 3392-3395 | Therefore, the dopant atom
of p-type material can be treated as core of one negative charge
along with its associated hole as shown in Fig 14 8(b) It is
obvious that one acceptor atom gives one hole |
9 | 3393-3396 | 14 8(b) It is
obvious that one acceptor atom gives one hole These holes are
in addition to the intrinsically generated holes while the source
of conduction electrons is only intrinsic generation |
9 | 3394-3397 | 8(b) It is
obvious that one acceptor atom gives one hole These holes are
in addition to the intrinsically generated holes while the source
of conduction electrons is only intrinsic generation Thus, for
such a material, the holes are the majority carriers and electrons
are minority carriers |
9 | 3395-3398 | It is
obvious that one acceptor atom gives one hole These holes are
in addition to the intrinsically generated holes while the source
of conduction electrons is only intrinsic generation Thus, for
such a material, the holes are the majority carriers and electrons
are minority carriers Therefore, extrinsic semiconductors doped
with trivalent impurity are called p-type semiconductors |
9 | 3396-3399 | These holes are
in addition to the intrinsically generated holes while the source
of conduction electrons is only intrinsic generation Thus, for
such a material, the holes are the majority carriers and electrons
are minority carriers Therefore, extrinsic semiconductors doped
with trivalent impurity are called p-type semiconductors For
p-type semiconductors, the recombination process will reduce
the number (ni)of intrinsically generated electrons to ne |
9 | 3397-3400 | Thus, for
such a material, the holes are the majority carriers and electrons
are minority carriers Therefore, extrinsic semiconductors doped
with trivalent impurity are called p-type semiconductors For
p-type semiconductors, the recombination process will reduce
the number (ni)of intrinsically generated electrons to ne We have, for p-type semiconductors
nh >> ne
(14 |
9 | 3398-3401 | Therefore, extrinsic semiconductors doped
with trivalent impurity are called p-type semiconductors For
p-type semiconductors, the recombination process will reduce
the number (ni)of intrinsically generated electrons to ne We have, for p-type semiconductors
nh >> ne
(14 4)
Note that the crystal maintains an overall charge neutrality
as the charge of additional charge carriers is just equal and
opposite to that of the ionised cores in the lattice |
9 | 3399-3402 | For
p-type semiconductors, the recombination process will reduce
the number (ni)of intrinsically generated electrons to ne We have, for p-type semiconductors
nh >> ne
(14 4)
Note that the crystal maintains an overall charge neutrality
as the charge of additional charge carriers is just equal and
opposite to that of the ionised cores in the lattice In extrinsic semiconductors, because of the abundance of
majority current carriers, the minority carriers produced
thermally have more chance of meeting majority carriers and
thus getting destroyed |
9 | 3400-3403 | We have, for p-type semiconductors
nh >> ne
(14 4)
Note that the crystal maintains an overall charge neutrality
as the charge of additional charge carriers is just equal and
opposite to that of the ionised cores in the lattice In extrinsic semiconductors, because of the abundance of
majority current carriers, the minority carriers produced
thermally have more chance of meeting majority carriers and
thus getting destroyed Hence, the dopant, by adding a large number of
current carriers of one type, which become the majority carriers, indirectly
helps to reduce the intrinsic concentration of minority carriers |
9 | 3401-3404 | 4)
Note that the crystal maintains an overall charge neutrality
as the charge of additional charge carriers is just equal and
opposite to that of the ionised cores in the lattice In extrinsic semiconductors, because of the abundance of
majority current carriers, the minority carriers produced
thermally have more chance of meeting majority carriers and
thus getting destroyed Hence, the dopant, by adding a large number of
current carriers of one type, which become the majority carriers, indirectly
helps to reduce the intrinsic concentration of minority carriers The semiconductor’s energy band structure is affected by doping |
9 | 3402-3405 | In extrinsic semiconductors, because of the abundance of
majority current carriers, the minority carriers produced
thermally have more chance of meeting majority carriers and
thus getting destroyed Hence, the dopant, by adding a large number of
current carriers of one type, which become the majority carriers, indirectly
helps to reduce the intrinsic concentration of minority carriers The semiconductor’s energy band structure is affected by doping In
the case of extrinsic semiconductors, additional energy states due to donor
impurities (ED) and acceptor impurities (EA) also exist |
9 | 3403-3406 | Hence, the dopant, by adding a large number of
current carriers of one type, which become the majority carriers, indirectly
helps to reduce the intrinsic concentration of minority carriers The semiconductor’s energy band structure is affected by doping In
the case of extrinsic semiconductors, additional energy states due to donor
impurities (ED) and acceptor impurities (EA) also exist In the energy band
diagram of n-type Si semiconductor, the donor energy level ED is slightly
below the bottom EC of the conduction band and electrons from this level
move into the conduction band with very small supply of energy |
9 | 3404-3407 | The semiconductor’s energy band structure is affected by doping In
the case of extrinsic semiconductors, additional energy states due to donor
impurities (ED) and acceptor impurities (EA) also exist In the energy band
diagram of n-type Si semiconductor, the donor energy level ED is slightly
below the bottom EC of the conduction band and electrons from this level
move into the conduction band with very small supply of energy At room
temperature, most of the donor atoms get ionised but very few (~1012)
atoms of Si get ionised |
9 | 3405-3408 | In
the case of extrinsic semiconductors, additional energy states due to donor
impurities (ED) and acceptor impurities (EA) also exist In the energy band
diagram of n-type Si semiconductor, the donor energy level ED is slightly
below the bottom EC of the conduction band and electrons from this level
move into the conduction band with very small supply of energy At room
temperature, most of the donor atoms get ionised but very few (~1012)
atoms of Si get ionised So the conduction band will have most electrons
coming from the donor impurities, as shown in Fig |
9 | 3406-3409 | In the energy band
diagram of n-type Si semiconductor, the donor energy level ED is slightly
below the bottom EC of the conduction band and electrons from this level
move into the conduction band with very small supply of energy At room
temperature, most of the donor atoms get ionised but very few (~1012)
atoms of Si get ionised So the conduction band will have most electrons
coming from the donor impurities, as shown in Fig 14 |
9 | 3407-3410 | At room
temperature, most of the donor atoms get ionised but very few (~1012)
atoms of Si get ionised So the conduction band will have most electrons
coming from the donor impurities, as shown in Fig 14 9(a) |
9 | 3408-3411 | So the conduction band will have most electrons
coming from the donor impurities, as shown in Fig 14 9(a) Similarly,
FIGURE 14 |
9 | 3409-3412 | 14 9(a) Similarly,
FIGURE 14 8 (a) Trivalent
acceptor atom (In, Al, B etc |
9 | 3410-3413 | 9(a) Similarly,
FIGURE 14 8 (a) Trivalent
acceptor atom (In, Al, B etc )
doped in tetravalent Si or Ge
lattice giving p-type semicon-
ductor |
9 | 3411-3414 | Similarly,
FIGURE 14 8 (a) Trivalent
acceptor atom (In, Al, B etc )
doped in tetravalent Si or Ge
lattice giving p-type semicon-
ductor (b) Commonly used
schematic representation of
p-type material which shows
only the fixed core of the
substituent acceptor with
one effective additional
negative charge and its
associated hole |
9 | 3412-3415 | 8 (a) Trivalent
acceptor atom (In, Al, B etc )
doped in tetravalent Si or Ge
lattice giving p-type semicon-
ductor (b) Commonly used
schematic representation of
p-type material which shows
only the fixed core of the
substituent acceptor with
one effective additional
negative charge and its
associated hole Rationalised 2023-24
Physics
332
EXAMPLE 14 |
9 | 3413-3416 | )
doped in tetravalent Si or Ge
lattice giving p-type semicon-
ductor (b) Commonly used
schematic representation of
p-type material which shows
only the fixed core of the
substituent acceptor with
one effective additional
negative charge and its
associated hole Rationalised 2023-24
Physics
332
EXAMPLE 14 2
for p-type semiconductor, the acceptor energy level EA is slightly above
the top EV of the valence band as shown in Fig |
9 | 3414-3417 | (b) Commonly used
schematic representation of
p-type material which shows
only the fixed core of the
substituent acceptor with
one effective additional
negative charge and its
associated hole Rationalised 2023-24
Physics
332
EXAMPLE 14 2
for p-type semiconductor, the acceptor energy level EA is slightly above
the top EV of the valence band as shown in Fig 14 |
9 | 3415-3418 | Rationalised 2023-24
Physics
332
EXAMPLE 14 2
for p-type semiconductor, the acceptor energy level EA is slightly above
the top EV of the valence band as shown in Fig 14 9(b) |
9 | 3416-3419 | 2
for p-type semiconductor, the acceptor energy level EA is slightly above
the top EV of the valence band as shown in Fig 14 9(b) With very small
supply of energy an electron from the valence band can jump to the level
EA and ionise the acceptor negatively |
9 | 3417-3420 | 14 9(b) With very small
supply of energy an electron from the valence band can jump to the level
EA and ionise the acceptor negatively (Alternately, we can also say that
with very small supply of energy the hole from level EA sinks down into
the valence band |
9 | 3418-3421 | 9(b) With very small
supply of energy an electron from the valence band can jump to the level
EA and ionise the acceptor negatively (Alternately, we can also say that
with very small supply of energy the hole from level EA sinks down into
the valence band Electrons rise up and holes fall down when they gain
external energy |
9 | 3419-3422 | With very small
supply of energy an electron from the valence band can jump to the level
EA and ionise the acceptor negatively (Alternately, we can also say that
with very small supply of energy the hole from level EA sinks down into
the valence band Electrons rise up and holes fall down when they gain
external energy ) At room temperature, most of the acceptor atoms get
ionised leaving holes in the valence band |
9 | 3420-3423 | (Alternately, we can also say that
with very small supply of energy the hole from level EA sinks down into
the valence band Electrons rise up and holes fall down when they gain
external energy ) At room temperature, most of the acceptor atoms get
ionised leaving holes in the valence band Thus at room temperature the
density of holes in the valence band is predominantly due to impurity in
the extrinsic semiconductor |
9 | 3421-3424 | Electrons rise up and holes fall down when they gain
external energy ) At room temperature, most of the acceptor atoms get
ionised leaving holes in the valence band Thus at room temperature the
density of holes in the valence band is predominantly due to impurity in
the extrinsic semiconductor The electron and hole concentration in a
semiconductor in thermal equilibrium is given by
nenh = ni
2
(14 |
9 | 3422-3425 | ) At room temperature, most of the acceptor atoms get
ionised leaving holes in the valence band Thus at room temperature the
density of holes in the valence band is predominantly due to impurity in
the extrinsic semiconductor The electron and hole concentration in a
semiconductor in thermal equilibrium is given by
nenh = ni
2
(14 5)
Though the above description is grossly approximate and
hypothetical, it helps in understanding the difference between metals,
insulators and semiconductors (extrinsic and intrinsic) in a simple
manner |
9 | 3423-3426 | Thus at room temperature the
density of holes in the valence band is predominantly due to impurity in
the extrinsic semiconductor The electron and hole concentration in a
semiconductor in thermal equilibrium is given by
nenh = ni
2
(14 5)
Though the above description is grossly approximate and
hypothetical, it helps in understanding the difference between metals,
insulators and semiconductors (extrinsic and intrinsic) in a simple
manner The difference in the resistivity of C, Si and Ge depends upon
the energy gap between their conduction and valence bands |
9 | 3424-3427 | The electron and hole concentration in a
semiconductor in thermal equilibrium is given by
nenh = ni
2
(14 5)
Though the above description is grossly approximate and
hypothetical, it helps in understanding the difference between metals,
insulators and semiconductors (extrinsic and intrinsic) in a simple
manner The difference in the resistivity of C, Si and Ge depends upon
the energy gap between their conduction and valence bands For C
(diamond), Si and Ge, the energy gaps are 5 |
9 | 3425-3428 | 5)
Though the above description is grossly approximate and
hypothetical, it helps in understanding the difference between metals,
insulators and semiconductors (extrinsic and intrinsic) in a simple
manner The difference in the resistivity of C, Si and Ge depends upon
the energy gap between their conduction and valence bands For C
(diamond), Si and Ge, the energy gaps are 5 4 eV, 1 |
9 | 3426-3429 | The difference in the resistivity of C, Si and Ge depends upon
the energy gap between their conduction and valence bands For C
(diamond), Si and Ge, the energy gaps are 5 4 eV, 1 1 eV and 0 |
9 | 3427-3430 | For C
(diamond), Si and Ge, the energy gaps are 5 4 eV, 1 1 eV and 0 7 eV,
respectively |
9 | 3428-3431 | 4 eV, 1 1 eV and 0 7 eV,
respectively Sn also is a group IV element but it is a metal because the
energy gap in its case is 0 eV |
9 | 3429-3432 | 1 eV and 0 7 eV,
respectively Sn also is a group IV element but it is a metal because the
energy gap in its case is 0 eV FIGURE 14 |
9 | 3430-3433 | 7 eV,
respectively Sn also is a group IV element but it is a metal because the
energy gap in its case is 0 eV FIGURE 14 9 Energy bands of (a) n-type semiconductor at T > 0K, (b) p-type
semiconductor at T > 0K |
9 | 3431-3434 | Sn also is a group IV element but it is a metal because the
energy gap in its case is 0 eV FIGURE 14 9 Energy bands of (a) n-type semiconductor at T > 0K, (b) p-type
semiconductor at T > 0K Example 14 |
9 | 3432-3435 | FIGURE 14 9 Energy bands of (a) n-type semiconductor at T > 0K, (b) p-type
semiconductor at T > 0K Example 14 2 Suppose a pure Si crystal has 5 × 1028 atoms m–3 |
9 | 3433-3436 | 9 Energy bands of (a) n-type semiconductor at T > 0K, (b) p-type
semiconductor at T > 0K Example 14 2 Suppose a pure Si crystal has 5 × 1028 atoms m–3 It is
doped by 1 ppm concentration of pentavalent As |
9 | 3434-3437 | Example 14 2 Suppose a pure Si crystal has 5 × 1028 atoms m–3 It is
doped by 1 ppm concentration of pentavalent As Calculate the
number of electrons and holes |
9 | 3435-3438 | 2 Suppose a pure Si crystal has 5 × 1028 atoms m–3 It is
doped by 1 ppm concentration of pentavalent As Calculate the
number of electrons and holes Given that ni =1 |
9 | 3436-3439 | It is
doped by 1 ppm concentration of pentavalent As Calculate the
number of electrons and holes Given that ni =1 5 × 1016 m–3 |
9 | 3437-3440 | Calculate the
number of electrons and holes Given that ni =1 5 × 1016 m–3 Solution Note that thermally generated electrons (ni ~1016 m–3) are
negligibly small as compared to those produced by doping |
9 | 3438-3441 | Given that ni =1 5 × 1016 m–3 Solution Note that thermally generated electrons (ni ~1016 m–3) are
negligibly small as compared to those produced by doping Therefore, ne »»»»» ND |
Subsets and Splits