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
N_D = 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?

V_bi = V_T ln[N_d1/N_D2] = 0.137V

The buried layer is at the higher potential.