Predict the effect on the electrical properties of a silicon crystal at room temperature (300 K) if every millionth silicon atom is replaced by an atom of indium. Given: concentration of atoms = 5 x 1028 m-3; intrinsic carrier concentration = 1.5 x 1016m-3; intrinsic conductivity = 4.4 x 10-4
Sm-1; intrinsic resistivity = 2300 W m
Suggested answer:
Concentration of silicon atoms = 5 x 1028 m-3
Hole concentration is increased by the amount
New electron concentration
= 0.45 1010 m-3
Electron concentration is reduced by the amount
Note that the electron concentration has decreased over its intrinsic concentration by the same amount with which the hole concentration has increased.
Conductivity,
s = (neme + nhmh)e
= (0.45 1010 0.135 + 5 1022 0.048) (1.6 10-19)
The contribution of electron to the conductivity is clearly negligible as compared to that of the holes.
The conductivity of silicon doped with indium is much larger than its intrinsic conductivity (0.00044 S m-1)
The resistive is 0.0026 Wm.
It is very small as compared to the intrinsic resitivity of 2300Wm.
The number of impurity atoms is one part per million which is very small as compared to the number of defects in crystals. It does not have much influence on other properties but the conductivity has increased by almost six orders of magnitude.
0.0026 Wm.
It is very small as compared to the intrinsic resitivity of 2300Wm.