DIRECT BAND GAP: In the direct band gap band to band recombination and generation occur. Band to band recombination: In band-to-band recombination electron from conduction band directly come back to valance band (in valance band holes are present which are the deficiency of electrons which are form when electrons leave valance band and go to conduction band) The electrons and holes annihilate each other the excess energy release during this process in the form of light called photon or in the form of thermal energy. Band to band recombination is called direct band recombination. Band to band generation: In band-to-band generation electron is excited directly from valance band in to the conduction band after absorbing the thermal energy or photon(light) as shown in fig. given bellow.  If the thermal energy is absorbed this process is called thermal generation  If the light is absorbed this process is called photo generation Momentum consideration in direct band: In the EK plot K is the parameter proportional to momentum of electron.  GaAs is a notable member of direct band semiconductor  Photons, being massless entities carry the little momentum. In direct band-band recombination K-value of electron’s and holes are all bounced k=o.as shown in figure given bellow, the little change in momentum is required for the recombination process to proceed. For conservation of energy and momentum simply the photon is emitted Energy and momentum have parabolic shape  

1. EXPERIMENT NAME:
“Theoretically investigate the nature of direct 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
full from electrons.in that type of band there is no free electron

3. 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. CONDUCTION
SEMICONDUCTOR
INDUCTOR

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
DIRECT BAND GAP:
In the direct band gap band to band recombination and generation occur.
Band to band recombination:
In band-to-band recombination electron from conduction band directly come back to
valance band (in valance band holes are present which are the deficiency of electrons
which are form when electrons leave valance band and go to conduction band) The
electrons and holes annihilate each other the excess energy release during this
process in the form of light called photon or in the form of thermal energy.
Band to band recombination is called direct band recombination.
Band to band generation:
In band-to-band generation electron is excited directly from valance band in to the
conduction band after absorbing the thermal energy or photon(light) as shown in fig.
given bellow.
 If the thermal energy is absorbed this process is called thermal generation
 If the light is absorbed this process is called photo generation

6. Band to band generation:
Band to band recombination:

7. Momentum considerationin directband:
In the EK plot K is the parameter proportional to momentum of electron.
 GaAs is a notable member of direct band semiconductor
 Photons, being massless entities carry the little momentum.
In direct band-band recombination K-value of electron’s and holes are all bounced
k=o.as shown in figure given bellow, the little change in momentum is required for
the recombination process to proceed.
For conservation of energy and momentum simply the photon is emitted
Energy and momentum have parabolic shape.