Determine the number density of donor atoms which have to be added to an intrinsic germanium semiconductor to produce an n-type semiconductor of conductivity `5Omega^(-1)cm^(-1)`, given that the mobility of electron in n-type germanium is `3900 cm^(2)V^(-1)s^(-1)`. Neglect the contribution of holes to conductivity.

Explanation

To determine the number density of donor atoms required to produce an n-type semiconductor with a specified conductivity, we can follow these steps:

### Step 1: Understand the relationship between conductivity, electron concentration, and mobility
The conductivity (\( \sigma \)) of an n-type semiconductor can be expressed using the formula:
\[ \sigma = n_e \cdot \mu_e \cdot e \]
where:
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