Unit 3. SOLID STATE PHYSICS
INTRODUCTION
Solid-state physics is the study of rigid matter or solids, through methods such
as quantum mechanics, crystallography, electromagnetism and metallurgy. It is the largest
branch of condensed matter physics. Solid-state physics studies how the large-scale properties of
solid materials result from their atomic-scale properties. Thus, solid-state physics forms a
theoretical basis of materials science. It also has direct applications, for example in the
technology of transistors and semiconductors.
HISTORY
The physical properties of solids have been common subjects of scientific inquiry for
centuries, but a separate field going by the name of solid-state physics did not emerge until the
1940s, in particular with the establishment of the Division of Solid State Physics (DSSP) within
the American Physical Society. The DSSP catered to industrial physicists, and solid-state
physics became associated with the technological applications made possible by research on
solids. By the early 1960s, the DSSP was the largest division of the American Physical Society.
Large communities of solid state physicists also emerged in Europe after World War II,
in particular in England, Germany, and the Soviet Union. In the United States and Europe, solid
state became a prominent field through its investigations into semiconductors,
superconductivity, nuclear magnetic resonance, and diverse other phenomena. During the early
Cold War, research in solid state physics was often not restricted to solids, which led some
physicists in the 1970s and 1980s to found the field of condensed matter physics, which
organized around common techniques used to investigate solids, liquids, plasmas, and other
complex matter. Today, solid-state physics is broadly considered to be the subfield of condensed
matter physics, often referred to as hard condensed matter that focuses on the properties of solids
with regular crystal lattices.
ENERGY LEVEL IN n-type AND p- type SEMICONDUCTOR
The n type and p type semiconductors are produced by addition of impurity in pure
semiconductor (Si, Ge). In n- type semiconductor materials, there are extra electron energy
levels near the bottom of conduction band and can easily exited into the conduction band. In p-
type semiconductor materials, extra holes energy level near to top of valence band allows
excitation of valence electrons.
DYPCET, Kolhapur Page 1
, Unit 3. SOLID STATE PHYSICS
FERMI DIRAC DISTRIBUTION
In conduction band, the distribution of an electron is OR its probability that electron
occupies energy level at thermal equilibrium is
1
f (E) ..........(1)
1 exp( E EF ) / kT
where, EF Fermi energy level of eletrons or holes
f ( E ) probability function
k=Boltzman constant
The above equation is also called as Fermi Dirac Distribution Function.The fermi energy of
conductor can be calculated at zero and elevated temperatures.
A) At 0 K, Figure shows the conduction band of conductor.
The electron distribution is from the bottom of conduction band to
upper level EF. Thus, fermi level is defined as “ The maximum
uppermost filled level in conductor at 0K”. Or the maximum
energy that free electrons can have in conductor at 0K.
(i) If energy level (E) lying below the EF then
E<EF= -Ve
1 1 1
f (E) ( E EF )
1
1 e / kT 1 e 1 0
i.e. All the energy levels are lying below EF are occupied by electron
(ii) If energy level (E) lying above the EF then E>EF= +Ve
DYPCET, Kolhapur Page 2
INTRODUCTION
Solid-state physics is the study of rigid matter or solids, through methods such
as quantum mechanics, crystallography, electromagnetism and metallurgy. It is the largest
branch of condensed matter physics. Solid-state physics studies how the large-scale properties of
solid materials result from their atomic-scale properties. Thus, solid-state physics forms a
theoretical basis of materials science. It also has direct applications, for example in the
technology of transistors and semiconductors.
HISTORY
The physical properties of solids have been common subjects of scientific inquiry for
centuries, but a separate field going by the name of solid-state physics did not emerge until the
1940s, in particular with the establishment of the Division of Solid State Physics (DSSP) within
the American Physical Society. The DSSP catered to industrial physicists, and solid-state
physics became associated with the technological applications made possible by research on
solids. By the early 1960s, the DSSP was the largest division of the American Physical Society.
Large communities of solid state physicists also emerged in Europe after World War II,
in particular in England, Germany, and the Soviet Union. In the United States and Europe, solid
state became a prominent field through its investigations into semiconductors,
superconductivity, nuclear magnetic resonance, and diverse other phenomena. During the early
Cold War, research in solid state physics was often not restricted to solids, which led some
physicists in the 1970s and 1980s to found the field of condensed matter physics, which
organized around common techniques used to investigate solids, liquids, plasmas, and other
complex matter. Today, solid-state physics is broadly considered to be the subfield of condensed
matter physics, often referred to as hard condensed matter that focuses on the properties of solids
with regular crystal lattices.
ENERGY LEVEL IN n-type AND p- type SEMICONDUCTOR
The n type and p type semiconductors are produced by addition of impurity in pure
semiconductor (Si, Ge). In n- type semiconductor materials, there are extra electron energy
levels near the bottom of conduction band and can easily exited into the conduction band. In p-
type semiconductor materials, extra holes energy level near to top of valence band allows
excitation of valence electrons.
DYPCET, Kolhapur Page 1
, Unit 3. SOLID STATE PHYSICS
FERMI DIRAC DISTRIBUTION
In conduction band, the distribution of an electron is OR its probability that electron
occupies energy level at thermal equilibrium is
1
f (E) ..........(1)
1 exp( E EF ) / kT
where, EF Fermi energy level of eletrons or holes
f ( E ) probability function
k=Boltzman constant
The above equation is also called as Fermi Dirac Distribution Function.The fermi energy of
conductor can be calculated at zero and elevated temperatures.
A) At 0 K, Figure shows the conduction band of conductor.
The electron distribution is from the bottom of conduction band to
upper level EF. Thus, fermi level is defined as “ The maximum
uppermost filled level in conductor at 0K”. Or the maximum
energy that free electrons can have in conductor at 0K.
(i) If energy level (E) lying below the EF then
E<EF= -Ve
1 1 1
f (E) ( E EF )
1
1 e / kT 1 e 1 0
i.e. All the energy levels are lying below EF are occupied by electron
(ii) If energy level (E) lying above the EF then E>EF= +Ve
DYPCET, Kolhapur Page 2
