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 (ni = 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.