CBSE 2025, Set 2

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.

Edvaya · Accepted Answer

The correct answer is Subjective. In a doped n-type semiconductor, the total number of conduction electrons is the sum of:
1. The electrons contributed by the pentavalent donor impurities (which are heavily majority).
2. The electrons generated intrinsically due to thermal agitation (breaking of covalent bonds).

However, the total number of holes is *only* due to the holes generated from the intrinsic sources (thermal agitation). Since the donor atoms supply a massive number of extra electrons, the electron concentration ($n_e$) far exceeds the hole concentration ($n_h$).

Furthermore, the large number of electrons increases the rate of recombination, which further suppresses the steady-state hole concentration below its intrinsic level, maintaining $n_e \gg n_h$.

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Physics > Modern Physics > Semiconductor Electronics

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