question_answer 55)

  Suppose a 'n'-type wafer is created by doping Si crystal having 5 x 1028 atoms/m3 with 1 ppm concentration of As. On the surface 200 ppm Boron is added to create 'P? region in this wafer. Considering   (i) Calculate the densities of the charge carriers in the n & p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

Answer:

                  (i) When As is implanted in Si-crystal, n-type  wafer is created. The no. of majority carrier electrons due to doping of A s, is                                 No. of minority carriers (holes ) in n-type wafer is                                 When B is implanted in Si ?crystal, p-type wafer is created with no of holes,                                 Minority carriers (electrons ) created in p-type wafer is                 (ii) When p-n junction is reverse biased, the minority carrier holes of n-region wafer  would contribute more to the reverse saturation current than minority carrier electrons    of p-region wafer.