Question 3

1.  

   
   

   (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.      
   (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.
   

   (c)        Holes and electrons.