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Semiconductor
Physics : - Coggle Diagram
Semiconductor
Physics :
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Types of semiconductor
Intrinsic Semiconductor
1.Pure semiconductor.
2.Charge carrier concentration.
3.Number of electrons = Number of holes.
Eg.Silicon
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Energy band
A gap between the lower most point of conduction band and upper most point of valence band.
Conduction band
1.The energy band involving the energy levels of valence electrons is known as the valance band.
2.It is the highest occupied energy band.
3.When compared with insulators,the bandage in semiconductors is smaller.
4.It allows the electrons in the valance band to jump into the conduction band on receiving any external energy.
Valence band
1.It is the lowest unoccupied band that includes the energy levels of positive (holes) on negative (free electrons) charge carriers.
2.It has Conducting electrons resulting in the flow of current.
3.The conduction band possess high energy level and are generally empty.
4.The conduction band in semiconductors accepts the electrons from the valance band.
Band gap & forbidden gap
1.The gap between adjacent bands representing a range of energies that possess no electron is called a forbidden gap.
2.The splitting up of sharp and tightly packed energy levels forms energy band.
Hall effect
If a metal or a semiconductor carrying a current I is placed in a transverse magnetic field B,a potential difference is produced in the direction normal to both the current and magnetic field directions. This phenomenon is called Hall effect.
Hall angle
The net electric field E in the semiconductor is a vector sum of Ex and Eh.It acts at an angle theta to the x-axis.Thetah is called the hall angle.
The equation is given by,
tanthetah= Uh.B.
Hall field
The transverse electric field Eh is known as Hall field.
The equation is given by,
Eh=Vh/w.
Hall coefficient
Hall field per unit current density per unit magnetic induction is called Hall coefficient.
The equation is given by
Rh=1/pe=Vht/BI.
Hall voltage
The Hall voltage is a real voltage and it can be measured with a voltmeter.
The equation is given by,
Vh=RhBI/t.
Law of Mass action
The law suggests that the addition of impurities to an intrinsic semiconductor increases the concentration of one type carrier, which consequently becomes majority carrier and simultaneously decreases the concentration of the other carrier, which as a result becomes minority carrier.
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Fermi energy
When the temperature rises above
absolute zero, these charge carriers will begin
to occupy states above fermi level.
Intrinsic fermi energy
1.The equation is given by,
Ef=Ec+Ev/2+3/4ktln(mh/me).
2.Now, Ef=Ev+Ec/2
3.Thus, the fermi level in a semiconductor lies at the center of the energy gap.
4.If the top of the valance band Ev is taken as zero level,
Ef=Eg/2.
Extrinsic fermi energy
N-type
1.In the low temperature region, electrons in the conduction
band are only due to the transitions of electrons from the donor levels.
2.The fermi level Efn lies between the donor level Ed the bottom edge of the conduction band Ec.
Efn=Ec+Ed/2 (Ionization region)
P-type
1.The fermi level Efp rises with increasing temperature from
below the acceptor level to intrinsic level Efi,
2.Efp=Ea+Ev/2 (Ionization region)
Efp=Ea(at T=Ts)
Efp=Eg/2 (Intrinsic region)
Conductivity
A semiconductor material has an electrical conductivity
value falling between that of a conductor and insulator.
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Extrinsic Conductivity
N-type
The equation is given by,
Conductivity n=NdeUe.
P-type
The equation is given by,
Conductivity p=NaeUh.
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