question_answer 41)

What is a semiconductor? Describe the two main types of semiconductors and contrast their conduction mechanism.

Answer:

Semiconductor is the solid which is perfect insulator at 0 K but conduct some electricity at room temperature. e.g., Silicon and Germanium. Two main types of semiconductors are n-type and p-type semiconductors. (i) n-type semiconductors. Silicon and germanium (Group 14) have very low electrical conductivity in the pure state. If we add certain elements like phosphorus (P) or arsenic (As) of group 15 to these covalent crystals, their atoms will also get linked with those of group 14 elements by covalent bonds but will have the extra electron which is not involved in the bonding (atoms have five valence electrons). These extra electrons will lead to electrical conductivity resulting in n-type semi conductors as these are conducting due to the movement of electrons. (ii) p-type semiconductors. If in the covalent crystals of group 14 elements, the addition of small amounts of the element aluminium (Al) or gallium (Ga) belonging to group 13 is done, the atoms of such elements can share only three electron with the atoms of group 14. Thus, the holes will be created in the lattice since there is no fourth electron available for sharing. The holes will lead to electrical conductivity and the crystals thus formed are also semiconductors. These are known as p-type semiconductors.