Properties of Semiconductors

Practice Questions:

Question 11: easy

A silicon (Si) specimen is doped with aluminium (Al). The concentration of acceptor atoms is \(10^{18}\text{ m}^{-3}\). Given that the intrinsic carrier concentration is \(10^{16}\text{ m}^{-3}\), the concentration of electrons in the specimen is

1. 10^{14} m^{-3}

2. 10^{16} m^{-3}

3. 10^{18} m^{-3}

4. 10^{12} m^{-3}

View Answer

Formula: \(n_e n_h = n_i^2\). Since the semiconductor is heavily p-doped, \(n_h approx N_a = 10^{18}\text{ m}^{-3}\). Therefore, \(n_e = frac{n_i^2}{n_h} = frac{(10^{16})^2}{10^{18}} = 10^{14}\text{ m}^{-3}\).

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Question 12: easy

Consider the following statements:

(a) At 0 K, semiconductor behaves as perfect conductor.

(b) Semiconductors have negative temperature coefficient of resistance.

Choose the correct statement.

1. Only (a)

2. Only (b)

3. Both (a) & (b)

4. Neither (a) nor (b)

View Answer

At 0 K, semiconductors behave as insulators since no electrons are in the conduction band. The resistance of a semiconductor decreases with increasing temperature, meaning it has a negative temperature coefficient of resistance. Thus, only statement (b) is correct.

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