Question 3
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(a) Explain the term doping with respect to semi-conductors.
(b) State the phase relationship between the input and output for each of the following:
(i) common emitter amplifier;
(ii) common collector amplifier;
(iii) common base amplifier.
(c) List the change carriers in a semi-conductor.The expected answers were:
(a) Doping is the process of adding impurity atoms (trivalent or pentavalent)
to an intrinsic semiconductor.(b) (i) for common emitter, there is 180º degree phase shift / in anti-phase.
(c) Holes and electrons.
(ii) for common base, there is no phase shift / 00 phase shift/ in phase.
(iii) for common collector, there is no phase shift/ 00 phase shift/ in phase.
Observation
A few Candidates could not recall that for semiconductors, the charge carriers are holes and electrons.