Physics 2015 JAMB Past Questions - Question 4: When impurities are added to semi-conductors, the conductivity of the semi-conductor

Correct Answer

D

Explanation

When impurities are added to semiconductors, the conductivity of the semiconductor can be altered. This process is known as doping. Doping can either increase or decrease the conductivity, depending on the type of impurity added.

There are two types of doping: n-type and p-type. In n-type doping, impurities with extra electrons, such as phosphorus or arsenic, are added to the semiconductor. These extra electrons create more free charge carriers, called electrons, which increase the conductivity of the semiconductor.

On the other hand, in p-type doping, impurities with fewer electrons, such as boron or gallium, are added to the semiconductor. These impurities create "holes" in the crystal lattice, which act as positive charge carriers. The presence of these holes increases the conductivity of the semiconductor.

By selectively doping different regions of a semiconductor, such as in a transistor or diode, it is possible to create complex electronic devices with specific electrical properties.