Explain about a charge density in a semiconductor
Answers
CHARGE CARRIERS IN SEMICONDUCTORS
Objectives:
• Discovery of the nature of charge carriers in intrinsic and extrinsic
semiconductors
• Finding on what, how and why densities of charge carriers in semiconductors
depend
• Calculation methods of of charge carrier densities in semiconductors
Content:
Charge carriers in intrinsic semiconductors
Nature of charge carriers
Fermi level in an intrinsic semiconductor
Densities of carriers
Charge carriers in extrinsic semiconductors
n-type semiconductors
p-type semiconductors
Compensation doping
Excess carriers and lifetime
Carefully refined semiconductors are called intrinsic semiconductors. .
In a silicon crystal each atom is surrounded by four neighbour atoms. At 0 K
all valence electrons take part in covalent bonding and none are free to move
through the crystal.
As the temperature increases, the lattice vibrations arise. Some of the energy
of the lattice vibrations is transferred to the valence electrons. If sufficient
energy is given to an electron, it leaves a bond and becomes free.
The jump of an electron from the
valence band to the conduction
band corresponds to the release
of an electron from covalent
bonding. The minimum energy
required for that is equal to the
width of the forbidden band.
If the width of the forbidden band is less, electrons are released at lower
temperature.
When an electron is released, a positively charged vacancy appears. This
vacancy may be considered as a positive hole.
According to the energy band diagram an uncompleted allowed energy level in
the valence band corresponds to a hole.
Hope it helps..