What is indirect band gap? In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy Indirect Recombination. For indirect band-gap semiconductors (e.g., Si), a direct recombination process that conserves both energy and momentum is not possible without lattice interaction (creating phonons) Indirect band gap band recombination occur in steps as shown in figure The optical band gap (Eg) value can be easily determined from absorption spectra and from Tauc Plot. (αhv)^n=k(hv-E_g) n=2 for direct transition n=1/2 for idirect transition For the direct band gap material, you have to plot (αhv)^2 vs. hv (energy in eV). Where, α is absorption coefficient (cm-1), hv is energy in eV. Then, the direct band gap energy, Eg, can be obtained by extrapolating the linear portion to (αhv)^2 = 0 in that graph. For the indirect band gap material, you have to plot (αhv)^(1/2) vs. hv (energy in eV). Where, α is absorption coefficient (cm-1), hv is energy in eV. Then, the indirect band gap energy, Eg, can be obtained by extrapolating the linear portion to (αhv)^(1/2) = 0 in that graph..   EMERGYBAND THEORY: The important energy bands given bellow;  Filled band  Valance band  Conduction band  Forbidden gap FILLED BAND: As clear the name it is the type of band which is near to nucleus and it is completely     full from electrons.in that type of band there is no free electron VALANCE BAND: The last band of the atom is the valance band electron of that band are called valance electrons. When the valance electrons.  Band of energy level which are closer to nucleus.  An e- in valance band, expenses strong of attraction from nucleus  It can not move freely when external electric field is applied  It is called bounded electron. CONDUCTION BAND: When the valance electro gains some energy then they leave that band and cross the energy gap which is called forbidden gap or forbidden energy and goes to conduction band then current flow from metal(semiconductor). The free electron that escapes and goes in conduction band such process is called conduction the electron of such band is called free electrons  Band of energy level which are far away from nucleus  The conduction band is the band of orbitals that are high energy and generally empty  An e- in the conduction band has weak influence of nucleolus and hence it can move free under the effect of applied electric field and thus it produces current, it is called free electrons. FORBIDDEN GAP/ENERGY GAP:  In solid state physics an energy gap or bandgap is an energy range in solid where no electron state can exist.  It generally refers to the energy difference between the top of the valance band to the bottom of the conduction band in insulator and semiconductor  

1. EXPERIMENT NAME:
“Theoretically investigate the nature of Indirect band gap of novel
materials”
INTRODUCTION:
In solid-state physics, a band gap, also called an energy gap, is an energy range in a
solid where no electronic states can exist. In graphs of the electronic band structure
of solids, the band gap generally refers to the energy difference (in electron volts)
between the top of the valence band and the bottom of the conduction band i
Novel materials
The materials which are used in the present era for the construction, engineering and
scientific purposes are called as novel materials
for e.g. if you were born in stone ages, then stone, wood will be the novel materials for
you
but in present era, everything you see around is novel from metal, stone, wood,
polymer, ceramics and even water.
Semiconductor material are also novel materials
THEORY:
EMERGYBAND THEORY:
The important energy bands given bellow;
 Filled band
 Valance band
 Conduction band
 Forbidden gap
FILLED BAND:
As clear the name it is the type of band which is near to nucleus and it is completely

3. full from electrons.in that type of band there is no free electron
VALANCE BAND:
The last band of the atom is the valance band electron of that band are called valance
electrons. When the valance electrons.
 Band of energy level which are closer to nucleus.
 An e- in valance band, expenses strong of attraction from nucleus
 It can not move freely when external electric field is applied
 It is called bounded electron.
CONDUCTION BAND:
When the valance electro gains some energy then they leave that band and cross the
energy gap which is called forbidden gap or forbidden energy and goes to conduction
band then current flow from metal(semiconductor).
The free electron that escapes and goes in conduction band such process is called
conduction the electron of such band is called free electrons
 Band of energy level which are far away from nucleus
 The conduction band is the band of orbitals that are high energy and generally
empty
 An e- in the conduction band has weak influence of nucleolus and hence it can
move free under the effect of applied electric field and thus it produces current,
it is called free electrons.
FORBIDDEN GAP/ENERGY GAP:
 In solid state physics an energy gap or bandgap is an energy range in solid
where no electron state can exist.
 It generally refers to the energy difference between the top of the valance band
to the bottom of the conduction band in insulator and semiconductor

4. CONDUCTOR
SEMICONDUCTOR
INSULATOR

5. INSULATOR SEMICONDUCTOR CONDUTOR
 Insulator is the material
in which current does
not flow easily
 Having gap of several
electron volt 2.g 6ev
 Wood, plastic etc. are
example of insulator
 semiconductor have
intermediate property of
both conductor and
insulator
 Have less forbidden
gap of e.g., 1ev
 Silicon and germanium
etc. are example of
semiconductor
 conductors that
material in which
current can flow
easily
 Have no energy gap
 Silver, copper, iron
etc. are example of
conductor
INDIRECT BAND GAP:
What is indirectband gap?
 In an indirect band gap semiconductor, the maximum energy of the
valence band occurs at a different value of momentum to the minimum in the
conduction band energy
 Indirect Recombination. For indirect band-gap semiconductors (e.g., Si), a
direct recombination process that conserves both energy and momentum is not
possible without lattice interaction (creating phonons)
 Indirect band gap band recombination occur in steps as shown in figure
The opticalband gap (Eg) value can be easily determined from
absorption spectraand from Tauc Plot.
(αhv)n
= 𝑘(ℎ𝑣 − 𝐸𝑔 )
n=2 for direct transition
n=1/2 for idirect transition
 For the direct band gap material, you have to plot (αhv)2
vs. hv (energy in eV).
Where, α is absorption coefficient (cm-1), hv is energy in eV. Then, the direct band

7.  gap energy, Eg, can be obtained by extrapolating the linear portion to (αhv)2
= 0 in
that graph.
 For the indirect band gap material, you have to plot (αhv)
1
2 vs. hv (energy in eV).
Where, α is absorption coefficient (cm-1), hv is energy in eV. Then, the indirect
band gap energy, Eg, can be obtained by extrapolating the linear portion
to (αhv)
1
2 = 0 in that graph..

8. Tauc Plot: