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Chapter 3
SOLID STATE CHEMISTRY
Lecture/Lession Plan
SOLID STATE CHEMISTRY
3.1
Concept of solid
Solid compounds have different characteristic in shape and size from liquid or gas. Solids are rigid,
malleable, incompressible due to the absence of translational and rotational motion of the atoms,
molecules and ions.They have definite malting point. On heating, the kinetic energy of the constituent starts vibrate on the equilibrium or mean position and after a certain limit the vibration
energy becomes more than the binding energy among the constituents, as a result the solids get
melt. The melting point of ionic solids are higher than amorphous solids due to strong electrostatic
force of attraction among the opposite ions in case of ionic solids. So solids are generally two types1) Crystalline solid
2) Amorphous solid
1) Crystalline solid:The main criteria of a solid to be crystalline is, ion constituents are arranged
in a regular three dimension fashion to get a particular geometry. It have sharp melting point
and called anisotropic solid. But, due to presence of thermal vibration of the constituent in the
crystalline solid the arrangement pattern of the constituent is seldom perfect. Due to presence of
thermal vibration of the constituents, some impurities and defects in crystalline solid influence different chemical properties of solids.
3.2
Defects or imperfection in crystalline solid
In a crystalline solid, the constituent particles, ions are arranged in regular fashion. But, this arrangement is completely perfect at 0K temperature. Above this temperature the arrangement of
constituents are imperfect or defective from their intrinsic arrangement. Again defects or imperfect
arrangements can be introduced in the crystal purposefully by adding some impurity from outside
into the crystal lattice. Due to presence of defects in the crystal, solids changes their chemical
properties (like colour, electrical conductivity and mechanical properties) as well as produce some
new properties also.
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Defects or imperfectness of crystal: Any deviation of arrangement of the constituent atoms or
molecules from their regular three dimension particular intrinsic geometry is called defect or imperfectness of crystal.
In crystal three types of defects are found. These are1) Atomic imperfection or Point defects
2) Line defects and
3) Plane defects.
3.3
(1)Atomic imperfections or Point defect
The defects in crystal is due to i) the missing of constituent atoms or molecules from their normal
crystal point or ii) constituent atoms or molecules leave from their intrinsic/own crystal point and
shifted to interstitial position in the crystal lattice or iii) shifting of any foreign particle in the crystal
point or interstitial position in the crystal.
Point defects or atomic imperfections are three types
i) Stoichiometric defect
ii) Non-stoichiometric defect
iii) Impurity defect
3.3.1
(1.a) Stoichiometric defect
The point defect in crystal occurs due to i)the missing of constituent atoms or molecules from their
normal crystal point or ii) constituent atoms or molecules leave from their intrinsic/own crystal point
and shifted to interstitial position in the crystal lattice. Stoichiometric number ratio of constituent
atoms or molecules are in same ratio is called Stoichiometric defects.
Such type of defect is also called intrinsic defect. Some times this type of defect is called thermodynamic defect as it depends on temperature. Stoichiometric defects are two typesi) Vacancy defect
ii) Interstitial defect
3.4
(1.a.a) Vacancy defect
The vacancy defect in crystal occurs due to the missing of constituent atoms or molecules from their
normal crystal point.
As some constituent atoms or molecules are missing from their crystal point density of solid decreases due to such type of vacancy defect.
3.5
(1.a.b) Interstitial defect
The interstitial defect in crystal occurs due to missing of constituent atoms or molecules from their
intrinsic/own crystal point and shifted to interstitial position in the crystal lattice.
The void space present in between the crystal points in the crystal is called interstitial position. As
some extra constituent atoms or molecules are present in the interstitial position in the crystal the
3.6. (1.A.A.A) SCHOTTKY DEFECT
7
density of solid increases due to such type of interstitial defect.
The above all defects are found in case of non-ionic crystalline solid.
Presence of stoichiometric defects in ionic crystal but electrical neutrality is present are mainly two
typesi) Schottky defect
ii) Frenkel defect
3.6
(1.a.a.a) Schottky defect
This type of crystal defect was discovered by German scientist Schottky in 1930. This is basically
vacancy defect and it is found mainly in MX type (as NaCl) of ionic crystal. If any number of cations
are missing from the cationic point and to maintain the electrical neutrality same number of anions
are missing from the anionic point in ionic crystal lattice, then Schottky defect arises. The missing
ion pairs are found on the crystal surface. Such type of missing of pair of opposite ions create holes
in crystal lattice.
The electrical neutrality as well as stoichiometric ratio is maintained in such type of defect. Due to
missing of ion pairs from the crystal lattice (actually present at the outer surface of the crystal) the
density of Schottky defected crystal always less than the ideal crystal.
The schottky defect is found in those ionic crystals which havei) High coordination number ii) size of cation and anion are approximately same. Examples: NaCl,
KCl, CsCl, KBr etc.
The number of schottky defect (NS ) present per cc is given byNS
W
S
−
= N × e 2KT
Where, N is the number of vacant site per cc
WS is the required work to form Scottky defect.
K is the gas constant
T is the absolute temperature.
3.7
(1.a.a.b) Frenkel defect
This defect was discovered by Russian scientist Frenkel in 1926. This defect is basically another
type of vacancy defect and it is found mainly in MX type (as AgBr) of ionic crystal. If any cation is
missing from the cationic point and the missing ions are occupied in the interstitial site then Frankel
defect arises.
The electrical neutrality as well as the stoichiometric ratio are maintained in such type of defect.
Due to presence of cation at interstitial site in crystal lattice the mass and density of Frenkel defected
crystal always same as the ideal crystal.
The Frenkel defect is found in those ionic crystals which havei) low coordination number ii) the size of cation is less than counter anion. Examples: Agcl, AgBr,
AgI, Zns etc.
The number of Frenkel defect (NF ) present per cc is given byNF
=
W
F
1
−
(NN/ ) 2 × e 2KT
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Where, N is the number of site vacant per cc
N/ is the number of alternative interstitial site per cc
WF is the required work to form Frenkel defect.
K is the gas constant
T is the absolute temperature.
Consequences of Schottky and Frenkel defects:
i) Presence of defect in the crystal leads to increase in electrical conductivity. When a potential
is applied an ion moves from its lattice site and occupy a nearby and creates a new hole another
nearby ions moves in to it.The process is continuing and hole moves from one end to another end as
a result the electricity is conducted throughout the crystal.
ii) The dielectric constant of the crystal increases as in Frenkel defect the cation occupy the interstitial
site causing closeness of similar charge.
Difference between Schottky defect and Frenkel defect
Schottky defect
1. Schottky defects occur due
to migration of equal number of
cation and anion from a lattice
site to the surface of the crystal
2. In Schottky defected crystal
the dielectric constant of
the crystal remain unchanged
3. Due to missing of ion pairs from
their original crystal point to the
outer surface the mass and density
of Schottky defected crystal decreases
4.Schottky defect is found in those
ionic crystal having high coordination
number and almost similar size
of both cation and anion
5. Examples: NaCl, KCl, CsCl, KBr etc.
3.8
Frenkel defect
1. Frenkel defects occur due
to migration of cation from its
lattice point to the interstitial
site of the crystal
2. In Frenkel defected crystal
the dielectric constant of
the crystal increses
3. Due to missing of cations from
their original crystal point to the
interstitial site, the mass and density
of Frenkel defected crystal remain same
4. Frenkel defect is found in those
ionic crystal having low coordination
number and cation size is
much smaller than anion size
5. Examples: Agcl, AgBr, AgI, ZnS etc.
(1.b)Non-stoichiometric defect
The point defect in ionic crystal is due to i) the change in stoichiometric ratio from their normal
crystal geometry or ii) the ratio of cation and anion in the crystal is differ from the ratio directed
by the chemical formula of the compound is called non-stoichiometric defects.
Due to such defect though there is difference in the number of cation and the anion but the crystal
carry electrical neutrality. Some times this type of compound is called Barthollied (by the name of
scientist Barthollet) compound. Examples:
Fe0.88 O, Cu1.87 S, Fe0.88 O
Non-stoichiometric defects is found in ionic crystal due to excess or deficiency of metal ions. Nonstoichiometric defects are two typesi) Metal excess defects
3.9. (1.B.A) METAL EXCESS DEFECT
9
ii) Metal deficiency defects
3.9
(1.b.a) Metal excess defect
The metal excess defect arises due to two following:
3.10
(1.b.a.a) Anion vacancies or F centers
When any constituent anion is missing from its own lattice point of an ionic crystal and to maintain
the electrical neutrality the vacancy of the lattice point is filled up by an electron then the defect is
called anion vacancy or F center.
From the figure it is clear that though the crystal is electrically neutral, there is excess of metal ion.
Such type of metal excess defect (due to anion vacancy) is found in those ionic crystal which show
the Schottky defects. Examples: Alkali metals halide like NaCl, KCl, CsCl, KBr etc. The anion
vacancies are produced when these halides are heated with excess of their constituent metal vapour.
The metal atom get deposited on the surface of the alkali halide crystal. The halide ions now move
into the surface and combine with metal atom form MX leaving e− . asM + X− → M+ X− + e−
Anion vacancy also called F-center because F is taken from the German word Fabre which means
colour. These F-center are associated with the colour of the compound and the intensity of the
colour increases with greater f-center. F-center crystals are paramagnetic in nature due to presence
of unpaired electron in the vacant site. When any light fall on the F-center it absorb light energy and
the electron promoted from valence band to conduction band becomes photo conductors actually it
is n-type semiconductor. Again, any heat fall on the F-center it absorb heat energy and it becomes
thermal conductor.
Question: The colour of NaCl is white, it becomes yellow when heated with Na vapour.
Why?
The metal Na atom get deposited on the surface of the NaCl crystal . The Cl− ions now move into
the surface and combine with metal atom form NaCl leaving e− asNa + Cl− → Na+ Cl− + e−
The electron in the F-center absorb light fallen on it and get excited. During transition of electron
from higher level to the ground level it radiate energy and we see the complementary yellow colour.
Question: The colour of KCl is white, it becomes lilac when heated. Why?
3.11
(1.b.a.b) Excess cation occupying interstitial sites
Sometimes the constituent anion converted to gas by leaving electron and the electron occupy the
interstitial site of the crystal. These type of formation of gas by constituent anion and hence excess
of cation which occupy the interstitial site of the crystal causing the constituent cation excess in the
crystal is called metal excess defect. In this case the electrical neutrality of the crystal is maintained
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CHAPTER 3. SOLID STATE CHEMISTRY
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also.
Such type of metal excess defect (due to cation in the interstitial site) is found in those ionic crystal
which show the Frenkel defects. Examples: ZnO, CdO, Fe2 O3 , Cr2 O3 etc.
Question: When ZnO is heated some amount of O2 is liberated and the colour of ZnO is transformed from white to yellow as well as its electrical conductivity increases. Why?
ZnO is white in colour. When ZnO is heated it undergoes chemical reaction by releasing electrons.
1
ZnO(s) → Zn++ + O2 (g) + 2e−
2
As a result some amount of O2 is liberated from ZnO and Zn+2 ion is produced which is trapped
in the interstitial site of the crystal. Here non-stoichiometric ZnO is formed and the electron in the
interstitial site absorb light fallen on it and get excited. During transition of electron from higher
level to the ground level it radiate energy and we see the complementary yellow colour as well as
enhanced electrical conductivity.
Question: Metal excess defected ZnO (due to excess cation occupying interstitial sites)is heated in
dioxygen and cooled to room temperature, the electrical conductivity decreases. Why?
1
Zn++ + O2 (g) + 2e− → ZnO(s)
2
Actually, some electrons from interstitial site are added to O2 and converted to O2− ions and these
O2− combine with Zn+2 ions to form ZnO. As a result of removal of electrons from interstitial site
electrical conductivity decrease.
Importance of Metal excess defects:
i)Crystal with metal excess defect are normally coloured due to presence of free electrons either
in lattice point or interstitial position. When any light fall on the F-center it absorb light energy
and the electron promoted to the higher energy levels giving the absorption band as a result they
are coloured. ii)Crystal with metal excess defect are normally conduct electricity and heat due to
presence of free electrons either in lattice point or interstitial position. When any light fall on the
F-center it absorb light energy and the electron promoted from valence band to conduction band
becomes photo conductors actually it is n-type semiconductor because the number of defects is very
small. Again, any heat fall on the F-center it absorb heat energy and it becomes thermal conductor.
3.12
1.b.b) Metal deficiency defect
When any constituent cation is missing from its own lattice point of an ionic crystal and create
a cationic vacant there or extra anions or negative charges occupy in the interstitial site and to
maintain the electrical neutrality the nearest neighbour cation reached to higher oxidation state by
gaining excess positive charge then the defect is called metal deficiency defect.
From the figure it is clear that though the crystal is electrically neutral, there is number of cation
less than anion. Such type of metal deficiency defect(due to cation vacancy) is found in those ionic
crystal which have different oxidation state. Examples are FeO, NiO, FeS etc.
Metal deficiency defect are two types:
3.13. (1.B.B.A) CATION VACANCIES
3.13
11
(1.b.b.a) Cation vacancies
In such type of metal deficiency defect the constituent cation is missing from its own lattice point
of an ionic crystal and create a cationic vacant there and to maintain the electrical neutrality the
nearest neighbour cation reached to higher oxidation state by gaining excess positive charge then
the defect is called metal deficiency defect.
Fig.
From the figure it is clear that though the crystal is electrically neutral, there is number of cation
less than anion. Such type of metal deficiency defect(due to cation vacancy) is found in those ionic
crystal which have different oxidation state. Examples are FeO, NiO, FeS etc.
3.14
(1.b.b.b) Extra anion in the interstitial site
In such type of metal deficiency defect extra anions or negative charges occupy in the interstitial site
and to maintain the electrical neutrality the nearest neighbour cation reached to higher oxidation
state by gaining excess positive charge then the defect is called metal deficiency defect. Normally,
due to large size of anion or negatively charged ion, it is very difficult to fit them in the interstitial
site in ionic crystal.
Fig.
From the figure it is clear that though the crystal is electrically neutral, there is number of cation
less than anion. Such type of metal deficiency defect(due to cation vacancy) is found in those ionic
crystal which have different oxidation state. There is no example of such compound.
Importance of Metal deficiency defects:
i) Due to absence of cation in the crystal or cation vacancy provide positive hole. Due to presence
of these holes an electron may be transferred in a particular direction in the structure at the same
time the positive hole migrate to the opposite direction of the electron flow produce p-type semiconductor.
ii) Due to absence of cation on the surface or cation vacancy provide the characteristic to the compound to acts as catalyst.
iii) Due to absence of cation on the surface or cation vacancy provide the characteristic of metallic
luster in compound like FeS.
3.15
Impurity Defect
Some time some small amount of foreign materials are present in pure crystal as impurities and
brings defect in crystal called impurity Defect.
3.16
Doping
The process by which small amount of foreign materials are introduced in pure crystal as impurities
to brings defect in crystal called doping.
The small amount of foreign materials are called substitutional impurity which (atoms or ions) are
introduced in pure crystal and they replace the atoms or ions from their lattice point the foreign
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impurities .
On the other hand the impurity (atoms or ions) which occupy the interstitial site in crystal, are
called interstitial impurity and the solid crystal is called interstitial solid solution. Examples are:
i) Na+ ion is replaced by Sr+2 if small amount of SrCl2 is added in molten NaCl is and allowed to
crystallization. In this case to get electrical neutrality each two Na+ ion is replaced by one Sr+2 ion
from the crystal. In the crystal one Sr+2 ion occupy the lattice point of one Na+ ion and lattice
point for other Na+ ion is vacant. So cation vacancy in the crystal is equal to the doped Sr+2 ion.
ii)Ag+ ion is replace by Cd+2 if small amount of CdCl2 is added in molten AgCl is and allowed to
crystallization. In this case to get electrical neutrality each two Ag+ ion is replaced by one Cd+2
ion from the crystal. In the crystal one Cd+2 ion occupy the lattice point of one Ag+ ion and lattice
point for other Ag+ ion is vacant.So cation vacancy in the crystal is equal to the doped Cd+2 ion.
Fig.
Electrical property of solid: On the basis of electrical conduction solid can be divided in to three
categoryi) Conductors
ii) Semiconductors and
iii) Insulator
i) Conductors: The solid materials through which electricity can pass easily are called conductors. Metals are very good conductor of electricity. Silver metal is the best conductor among the
metals. The free electrons present in the metal are responsible for the conduction. For this reason
metals are also called electronic conductor. Copper(Cu), Aluminium(Al), Platinum(Pt), Gold(Au)
etc.areexamples of conducting materials. The normal value of electrical conduction of the metals
are in the order of 108 ohm−1 .m−1 .
ii) Semiconductors:The solid materials through which electricity do not pass easily are called
semiconductors. Their electrical conducting power in between good conductors and insulator. These
materials are called semiconductor. Germanium(Ge), Silicon(Si) metals and some other metal oxides like Cu2 O, CuO, Fe2 O3 , FeO and Cr2 O3 are examples of semiconductors. The normal value of
conductivity of semiconductors are in the order 104 ohm−1 .m−1 .
iii) Insulator: The solid materials through which electricity do not pass are called insulator. Their
electrical conducting power is really zero. Wood, bricks, some plastics, rubber and Mica etc. are examples of insulators. The normal value of conductivity of insulators are less than 10−20 ohm−1 .m−1 .
Band theory: Metals are usually crystalline with common coordination number twelve (12). Actually the metals atoms are linked by a special type of bonds known as metallic bond. In metal
the atoms loose the valence shell electrons and become positive charge. The released electrons are
not bound up with any particular metal ion, means the matrix of positive ions remains embedded
in a sea of mobile electrons. The band theory explains the position of these mobile electrons and
the process of electrical conduction. In crystal, when they occupy a definite positions, the electrons
are subjected to a non-uniform electric field. The electrons may now take position in the band.The
band however non-continuous, but separated by forbidden zones.
In metals, due to high coordination number, valence shell electrons are not sufficient for pairing
with all surrounding atoms to form covalent bonding. Hence, the lower bands are filled up first but
the upper band are farthest from from the nucleolus and they are empty or partially filled due to
insufficient electrons. The lower energy band is called valence band and the upper energy band is
called conduction band. The metallic bond structure can be explain by the help of molecular orbital
theory. In case of metallic compound molecular theory is called band theory. According to molecular
orbital theory, two molecular orbital are formed by the combination of two atomic orbital. Out of
these two molecular orbital the energy of one orbital is lower than the energy of each atomic orbital,
which is called bonding molecular orbital. The other molecular orbital have higher energy than the
3.17. SEMICONDUCTOR
13
atomic orbital and called antibonding molecular orbital.
The electrical conduction in metals will takes place when the valence shell is partly full, or the
valence and conduction bands are overlap. In case of valence shell is completely filled and there is
overlap between valence band and conduction band on application of a potential, the valence band
electron will not move and acceptance of electrons will also be forbidden. In such case the partially
filled or unfilled electrons in the conduction band may shift to a slightly higher level in the same
band. Thus there becomes a possibility of the transfer of electrons from one atom to another atom,
which will lead to electrical conduction.
Metals are good conductor electricity and the electrical conduction of the metals are in the order of
108 ohm−1 .m−1 .
In case of insulator every atoms is covalently linked with the nearest surrounding atoms and hence
the valence band is completely filled and perturbation within the band are imposable with an appreciable difference in energy gap (band gap) between the valence and conduction band.
Electrons therefore cannot be promoted and if very high electrical potential be applied there will
be rupture of the crystal instead of conduction. The normal value of conductivity are in the order
10−22 ohm− .m− .
In case of semiconductor a small amount of electric current can flow at room temperature and the
normal value of conductivity of semiconductors are in the order 102 to10−9 ohm−1 .m−1 .
With rise in temperature the electrical conduction of semiconductor increases due to transition of
electron from valence band to the conduction band.
3.17
Semiconductor
Semi-conductors are solid metal having electrical conducting power in between metal conductors
and insulator.
In semiconductors such as silicon and germanium, valence band is also filled. However, the band gap
between the filled up valence band and the nearest conduction band is small. At room temperature,
kinetic energy associated with electrons is sufficient to promote some electrons to the conduction
band and a small degree of electrical conductivity is shown by the semi conductor. Electrical conductivity of semiconductors increase with increase in temperature, since more electron can jump to
the conduction band. Examples are Germanium(Ge), Silicon(Si) metals and some metal oxides.. On
the basis of mechanism of conduction semiconductors are two typesi) Intrinsic semiconductor
ii) Extrinsic semiconductor
3.17.1
Intrinsic Semiconductor
Semiconductors are the solids which are perfect insulators at absolute zero. However they conduct
electric current at room temperature in pure state. Silicon(Si) and Germanium(Ge) are important
two examples of semiconductors. Pure Silicon and germanium crystallizes with similar pattern like
diamond in which each atom is bonded to four other atoms. At room temperature the conductivity
of either silicon or germanium is extremely low, since there is no free or conducting electrons in
metals. However, at higher temperatures, the crystal bonding breaks down, electrons are ejected
and are able to move through the crystal structure. Hence the conductivity increases. The materials
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CHAPTER 3. SOLID STATE CHEMISTRY
LECTURE/LESSION PLAN
which show such type of semi conduction without any external materials called intrinsic semiconductor. This type of conduction is called intrinsic conduction as it can be introduced in the crystal
with out adding any external materials. Conductivity of intrinsic semiconductors being very low,
they have no practical use. However their conductivity can be increased by adding an appropriate
amount of impurity.
3.17.2
Extrinsic semiconductor due to added impurities
Silicon and germanium (group 14 elements) in pure state have very low electrical conductivity.
However, the electrical conductivity of those elements can be improved by adding small amount of
impurities (mainly elements of group 13 or group 15). These impurities are called doping agent or
dopant. Appropriate doping agent increase the conductivity of semiconductors upto 104 times. Doping enhances the conductivity of semiconductor and called extrinsic semiconductor. The increase in
conduction is due to participation of impurity elements in between the valence band and conduction
band and thus making a bridge through which electrons can jump easily from the valence band to
the conduction band. For example, addition of boron to silicon at the rate of one atom per million
of silicon atoms, increase the conductivity by a factor of approximately one hundred thousand (from
4 × 108 ohm−1 cm−1 to 0.8 ohm−1 cm−1 at room temperature). Semiconductors are used in transistors, photoelectric devices and rectifiers.
3.18
Types of semiconductor
There are two types of semiconductori) n-type semiconductor
ii) p-type semiconductor
3.19
(i) n-type semiconductor
Here n stands for negative. n-type semiconductors are obtained due to metal excess defect or by
adding trace amount of group 15 elements [like phosphorous(P), Arsenic(As), Antimony(Sb)] having
electronic configuration ns2 np3 to extremely pure silicon or germanium by doping. The valency of
Germanium(Ge), Silicon(Si) is 4. Each Germanium(Ge), Silicon(Si) atom in the crystal is attached
with 4 atom of respective metal by 4 covalent bond. When an element of group 15 (let As) is
added to germanium (group 14) crystal, keeping the same crystal structure, some of the atoms of
germanium are replaced by arsenic. In such case four electrons out of 5 valence electrons of impurity
element (let P) is used in forming covalent bonds to 4 atoms of germanium while the fifth electrons
remains unused.
This extra electron can serve to conduct electricity as in case of metals. Here group 15 element
(P, As, Sb, Bi) is called donor. As a result germanium containing impurities of arsenic, it is arsenic
doped germanium which exhibit fairly high electrical conductivity. Silicon doped with a group 15
element (P, As, Sb, Bi) is called an n-type semiconductor. Here n standing for negative since electrons are used for the conduction of electricity.
3.20. (II) P-TYPE SEMICONDUCTOR
3.20
15
(ii) p-type semiconductor
Here p stands for positive. p-type semiconductors are obtained due to metal deficiency defect or by
doping with impurity atoms containing less electron (element of group 13) than the parent insulator to the lattice of an insulator. On adding trace amount of group 13 elements [like boron(B),
gallium(Ga) or indium(In)] having electronic configuration ns2 np1 to extremely pure Silicon or
germanium by doping. The valency of Germanium(Ge), Silicon(Si) is 4. Each Germanium(Ge),
Silicon(Si)atom in the crystal is attached with 4 atom of respective metal by 4 covalent bond. When
an element of group 13 (let In) is used in forming covalent bonds to 3 atoms of germanium while
there is a short of electron to form 4th bond to the neighbour germanium indium atoms are not able
to fully satisfy the tetra valency of germanium because they have one electron less than germanium.
Hence some of the sites which were normally occupied by the electrons, will be left unoccupied.
This gives rise to electron vacancies, commonly known as positive holes, because the net charge at
these site is positive. On application of the electric field, electrons from adjacent sites move into the
positive holes resulting in the formation of new positive holes and thus this phenomenon continues
and current is carried through out the crystal lattice. Here group 13 element (B, Al, Ga, In) is
called acceptor. Thus doping of germanium crystal with boron, indium and Gallium increase the
conductivity of germanium. Since the current in this case is carried due to the migration of positive
holes, this type of conduction is called p-type semiconductor..
p-type semiconductor
1. These are the intrinsic semiconductors which
have been doped by a trivalent element like Boron
2. In these semiconductors, conduction is mostly
by transfer of positive hole
3. Such type of semiconductors is produced
due to metal deficiency defect
4. In these semiconductors, there is excess of electrons
5. In these semiconductors, conduction
is due to positive electric charge
n-type semiconductor
1. These are the intrinsic or pure crystalline which
have been doped by a trivalent element like arsenic
2. In these semiconductors, conduction is mostly
by transfer of free electrons
3. Such type of semiconductors is produced
due to metal excess defect
4. In these semiconductors, there is excess of holes
5. In these semiconductors, conduction
is due to negative electric charge