Question

Identify the property which is not characteristic for a semiconductor ?
(A) at a very low temperatures, it behaves like an insulator
(B) at higher temperatures two types of charge carries will cause conductivity
(C) The charge carriers are electrons and holes in the valence band at higher temperatures.
(D) The semiconductor is electrically neutral.

Answer 1

Hint Understand the definition of a semiconductor. Semiconductors are materials that have partial characteristics of a pure conductor and partial characteristics of a pure inductor. The conductance of a semiconductor varies on the current and voltage applied to the electrode.

Complete Step By Step Solution
 Semiconductors possess certain electrical properties. Electrical properties are broadly classified as conductivity and resistivity. The resistivity of the semiconductor directly depends upon the temperature it is exposed to. Since, conductors allow electricity and heat to flow through and hence possess low resistance whereas at any temperature insulators possess high resistivity. At a low temperature, there won’t be any current passing through the semiconductor, hence behaves as insulators. Thus , the first option is a property of the semiconductor.
 When the temperature exposed to semiconductors is higher than the room temperature, the semiconductors will start to conduct , due to the reduction in the energy gap present between the conduction band and the valence band. When the energy gap is eliminated, the charges come together and flow towards each other.

At higher temperatures, the energy gap will get reduced causing the valence band to move closer towards the conduction band. Hence the flow of charge carriers will be from the valence band to the conduction band and both the holes and electrons are in the conduction band and not valence band. Hence, option (c) is wrong.
 Semiconductors have properties that lie in between conductors and insulators. The number of holes and number of electrons in a semiconductor are considered almost equal.

Hence, Option (c) is the right option .

Note Some properties of semiconductors depend upon the dopants that are added on to it. A n-type semiconductor will have 5 valent dopant material doped on it and whereas p-type doping will have 3 valent dopant doped on it.