Physics for Electronics Engineering: Unit III: Semiconductors and Transport Physics
Variation of Carrier Concentration with Temperature and Impurity
In extrinsic semiconductor, the resistivity decreases linearly with increase in temperature. This variation is considered under three different regions.
VARIATION OF CARRIER CONCENTRATION WITH TEMPERATURE AND IMPURITY
In
extrinsic semiconductor, the resistivity decreases linearly with increase in
temperature. This variation is considered under three different regions.
i)
Extrinsic or impurity range
ii)
Exhaustion range
iii)
Intrinsic range
For
a n-type semiconductor, the variation of carrier concentration n and p with
temperature is shown in fig. 3.11.
At
OK, both conduction and valence bands are free from any charge carriers and
hence, the electrical conductivity is zero.
With
increase in temperature, the donor atoms get ionised and hence electron
concentration in conduction band increases with temperature until all the donor
atoms are ionised. This range is known as impurity or extrinsic range.
When
the temperature is further increased to room temperature, there are no more
donor atoms to be ionised and hence the concentration of electrons in
conduction band remains constant over a certain temperature range. This region
is known as exhaustion range.
As
the temperature is increased further, the electrons in valence band are lifted
across the forbidden gap to conduction band. Thus, electron concentration
increases in conduction band considerably.
With
further increase in temperature, more and more electrons from valence band
reach conduction band and completely out-number the donor electrons.
The
material practically becomes intrinsic and so this range is called intrinsic
range. All these ranges are shown in fig. 3.11.
The dotted curve indicates hole concentration in an intrinsic range.
Table 3.4
Differences between intrinsic and
extrinsic semiconductors
Table 3.5
Differences between n type and
p-type semiconductors
Physics for Electronics Engineering: Unit III: Semiconductors and Transport Physics : Tag: : - Variation of Carrier Concentration with Temperature and Impurity
Physics for Electronics Engineering: Unit III: Semiconductors and Transport Physics
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Physics for Electronics Engineering
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