An electric field is applied to a slab of impure silicon. The majority carriers

Question

An electric field is applied to a slab of impure silicon. The majority carriers move in the same direction as the field. Is the principle impurity more likely phosphorus or aluminum? Q2. The number of charge carriers N is measured for two materials as a function of temperature and plotted on the graph as curves a and b. Which curve is for the metal, and which is for the semiconductor? Q3. A current of 1. 0 A is observed in a 1. 0 cm length of niobium nitride wire of cross-section 1. 0 mm^2. The temperature of the wire is 15 K (-258 C). If the critical temperature of niobium nitride is 16 K, what is the potential difference between the ends of the wire?

Explanation / Answer

1. If Phosphorous is added to pure silicon it would behave as a N- type semiconductor whereas if aluminium is added it becomes a P- type semiconductor. Since in the field the behavior is of P-type, aluminium is added to silicon.

2. 'b' is a semiconductor because in semiconductors as the temperature is increased more number of carriers make it to the conduction band (as a result of incresed energy). 'a' is metal.

3. Since temperature is below critical temp the wire will behave as a superconductor. Hence resistivity =0.

So there will be no potential difference between the ends.

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