Question

In an n-type semiconductor, electron-hole combination is a continuous process at room temperature. Yet the electron concentration is always greater than the hole concentration in it. Explain.

Hint:

Doping determines the majority charge carrier. In an \( n \)-type semiconductor, added donor atoms supply extra electrons, ensuring electrons outnumber thermally generated holes.

Answer 1

In an \( n \)-type semiconductor, a pentavalent impurity, such as phosphorus or arsenic, is introduced into an intrinsic semiconductor like silicon. Each impurity atom contributes an extra electron, thus elevating the free electron count in the conduction band. At ambient temperature, thermal energy continually produces electron-hole pairs, which subsequently recombine. Nevertheless, the electron concentration consistently exceeds that of holes due to the following reasons:

• Electrons are the dominant charge carriers in an \( n \)-type semiconductor, a consequence of doping.
• Holes, the minority carriers, are generated thermally and are significantly less numerous.
• Despite ongoing recombination, the substantial quantity of donated electrons sustains a higher equilibrium electron concentration.

Consequently, even with continuous recombination at room temperature, the electron population in an \( n \)-type semiconductor remains substantially greater than the hole population.