When an electric field is applied across a semiconductor

Options

A. electrons move from lower energy level to higher energy level in the conduction band
B. electrons move from higher energy level to lower energy level in the conduction band
C. holes in the valence band move from highest energy level to lower energy level.
D. holes in the valence band move from lower energy level to higher energy level.

Answer

A, C

Explanation

At room temmperature, electrons in conduction band in the crystalline structure of semi-conductor, move randomly and quite freely. When electric field is applied, they are accelerated, i.e. their energy increases and so they transit from lower energy level to higher energy level.
`rArr` Option (A) is correct.
Similarly, at room temperature, bound electrons in valence band of crystalline structure of semiconductor, move from one to another bound state. When electric field is applied they also get accelerated and they also get energy. Hence they move within the valence band, from low to high energy level. But we know that motion of hole seems to be opposite to that of bound electron. Hence, hole seems to be moving from higher to lower energy level.
`rArr ` Thus option (C ) is also correct.