ELE533 Bipolar Devices

Mid Term Exam
October 25, 2005


    Figure 3

  1. Consider the nn+ junction shown in Figure 3. (This represents the epi-buried layer junction.) The n type epi is doped with ND = 5 X 1015 donors/cm3. The doping level in the n+ buried layer is 1017 donors/cm3.

  2. What is the equilibrium voltage of the EPI relative to the burried layer?
  3. V2 - V1 = VT ln[ n2 / n1]

    where V2 is the EPI voltage and n2 is the EPI doping.

    VEPI - Vbl = 0.0259 ln[5x1015 / 1017 ] = - 77.6 mV

    The burried layer is at the higher potential.