ELE533 Bipolar Devices
Mid Term Exam
October 25, 2005
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.
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.