SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

300 CHAPTER 6. BIPOLAR JUNCTION TRANSISTORS

ND

W

A

ND/2

W

B

0 2W 0 2W

Figure 6.30: Figure for problem 6.38.

p

++

i n n

++

0.4 μm 0.1 μm

Figure 6.31: Figure for problem 6.39

1. Draw the band diagram of this base collector junction at zero bias. Assume that the
   base is heavily doped so that the entire voltage falls in the collector region. The
   built-in voltage is 1.4 eV.


2. Since theΓ−Lvalley spacing in GaAs is 0.3 eV, we would like to make the voltage
   drop in the intrinsic collector adjacent to the base to be equal to that number. This
   would lead to high electron velocities without intervalley transfer. Is it possible to
   achieve this by adding a single sheet of acceptors or donors to this structure? Draw
   charge, electric field and energy band profiles to explain your answer. Calculate the
   acceptor or donor sheet charge density you would use.