| S.No. |
Intrinsic semiconductor |
p-type semiconductor |
| (i) |
It is a semiconductor in pure form. |
It is a semiconductor doped with p-type (like Al,In) impurity. |
| (ii) |
Intrinsic charge carriers are electrons and holes
with equal concentration. |
Majority charge carriers are holes and minority
charge carriers are electrons. |
| (iii) |
Current due to charge carriers is feeble (of the
order of μA). |
Current due to charge carriers is significant (of the order of μA). |
p-Type semiconductor is electrically neutral because every atom, whether it is of pure semiconductor (Ge or Si) or of impurity (Al) is electrically neutral.
(b) If p-type and n-type semiconductor are heavily doped. Then due to diffusion of electrons from n-region to p-region, and of holes from p-region to n-region, a depletion region formed of size of order less than 1μm. The electric field directing from n-region to p-region produces a reverse bias voltage of about 5V and electric field becomes very large.
Explanation of voltage regulator. If reverse bias voltage V reaches the breakdown voltage VZ of zener diode, there is a large change in the current. After that (just above VZ there is a large change in the current by almost insignificant change in revese bias voltage. This means diode voltage remains constant.
For example: If unregulated voltage is supplied at terminals A and B, and input voltage increases, the current through resistor RZ and diode also increases. This current increases the voltage across RZ without any change in the voltage across diode. Thus, we have a regulated voltage across load reistor RL.
