Question:

a). Draw the energy diagram of a pn junction:
(i) at thermal equilibrium,

(ii) when a forward bias with magnitude half the built in potential (V = φk/2) is applied and

(iii)  when a  reverse bias of magnitude ten times the built in potential  (V = -3φk) is applied.

b).  With the aid of diagrams, describe how a space charge region is formed in a pn junction and how its width varies with an external bias.

c).  An abrupt silicon (n_i = 10¹⁰ cm^-3) pn junction consists of a p-type region containing 10¹⁷ cm^-3 acceptors along with 10¹⁶ cm^-3 donors and an n-type region containing 5 x 10¹⁶ cm^-3 donors along with 10¹⁵ cm^-3 acceptors. Calculate the total width of the depletion region if the applied voltage, V, equals 0, 0.5 and -2.5 V. Assume Vt = 25meV.