Question

If a pure silicon crystal has 1 million free electrons inside it, how many holes does it have? What happens to the number of free electrons and holes if the ambient temperature increases?

Answer 1

Explanation: 1) In pure silicon number of free electron is equal to number of holes.

2) A pure silicon behave as perfect insulator.

3) In pure silicon all electron and holes lies in the valance band there is no free electron in conduction band

4) therefore number of holes in pure silicon is equal to 1 millions.

Effect of Increasing temperature:

1) if the temperature is increases some free electron moves to conduction band from valance band .

2) These free electron create a holes in valance band

3) As further temperature increases more free electron moved to conduction band and more holes are generated.

4) in semiconductor if the temperature is increases conductivity increases.because temperature coefficient of semiconductor is negative.

5) upto certain temperature conductivity increses.beyond this temperature conductivity decreases due increase in randomness of more free electron. And thus temperature of crystal increase and may be damaged.

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