ELE533 Bipolar Devices

Mid Term Exam
July 9, 1998

Question 3 Answer

Consider a consider the nn+ junction shown in figure 1. (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 1018 donors/cm3.

What is the built-in potential between the n and n+ regions?
Vbi = VT ln[Nd1/ND2] = 0.137V
The buried layer is at the higher potential.