Condensed Matter - Conductor and Semiconductor

Which of the following statements concerning the electrical conductivities at a room temperature of a pure copper sample and a pure silicon sample is NOT true? 

1. The conductivity of the copper sample is many orders of magnitude greater than that of silicon sample.
2. If the temperature of the copper sample is increased, its conductivity will decrease.
3. If the temperature of the silicon sample is increased, its conductivity will increase.
4. The addition of an impurity in the copper sample always decreases its conductivity.
5. The addition of an impurity in the silicon sample always decreases its conductivity.

(GR8677 #23)

Solution:

A. TRUE.
Copper → good conductor
Silicon → semi conductor

B. TRUE.
Conductivity is the inverse of resistivity, 
Copper → good conductor → resistivity, → , decreases.

C. TRUE.
Silicon → semi conductor → resistivity, → , exponentially increases

D. TRUE.
For conductor, doping will decrease conductivity.

E. FALSE.
For semiconductor, doping increases the charge carrier density (electron or electron holes) in the conduction band → increasing conductivity

Answer: E