Question
Explain electricity conduction in intrinsic semi-conductors.
✓
Answer
→As shown in Fig. (a), Suppose there is a hole at site-1. The movement of holes can be visualised as shown in the Fig (b).
→An electron from the covalent bond at site-2, may jump to the vacant site-1. (hole)
→Thus, after such a jump, the hole is at site-2 and the site-1 has now an electron. Therefore, apparently, the hole has moved from site-1 to site-2. (So, the directions of motion of a hole and an electron are opposite).
→Note that the electron originally set free (Fig. a) is not involved in the process of hole motion.
→The free electron moves completely independently as conduction electron and gives rise to an electron current, I under an applied electric field.
→Remember that the motion of hole is only a convenient way of describing the actual motion of bound electrons, whenever there is an empty bond anywhere in the crystal.
→Under the action of an electric field, these holes move towards negative potential giving the hole current, $I _h$.
→The total current, I is thus the sum of electron current $I _e$ and the hole current $I _h$ :
$\therefore I = I _e+ I _h$ .......(1)
→Apart from the process of generation of conduction electrons and holes, a simultaneous process of recombination occurs in which these electrons recombine with holes.
→At equilibrium, the rate of generation is equal to the rate of recombination of charge carries. The recombination occurs due to an electron colliding with a hole.
→An electron from the covalent bond at site-2, may jump to the vacant site-1. (hole)
→Thus, after such a jump, the hole is at site-2 and the site-1 has now an electron. Therefore, apparently, the hole has moved from site-1 to site-2. (So, the directions of motion of a hole and an electron are opposite).
→Note that the electron originally set free (Fig. a) is not involved in the process of hole motion.
→The free electron moves completely independently as conduction electron and gives rise to an electron current, I under an applied electric field.
→Remember that the motion of hole is only a convenient way of describing the actual motion of bound electrons, whenever there is an empty bond anywhere in the crystal.
→Under the action of an electric field, these holes move towards negative potential giving the hole current, $I _h$.
→The total current, I is thus the sum of electron current $I _e$ and the hole current $I _h$ :
$\therefore I = I _e+ I _h$ .......(1)
→Apart from the process of generation of conduction electrons and holes, a simultaneous process of recombination occurs in which these electrons recombine with holes.
→At equilibrium, the rate of generation is equal to the rate of recombination of charge carries. The recombination occurs due to an electron colliding with a hole.
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