302 CHAPTER 6. BIPOLAR JUNCTION TRANSISTORS
Problem 6.3Consider anpnSi-BJT at 300 K with the following parameters:
Nde =10^18 cm−^3
Nab =10^17 cm−^3
Ndc =10^16 cm−^3
Db =30.0cm^2 s−^1
Lb =10. 0 μm
Wb =1. 0 μm
De =10cm^2 s−^1
Le =10. 0 μm
emitter thickness = 1. 0 μm
device area = 4. 0 × 10 −^6 cm
(a) Calculate the emitter efficiency and gainβwhen the EBJ is forward biased at 1.0 V and
the BCJ is reverse biased at 5.0 V.
(b) Calculate the output conductance of the device defined by
go=
ΔIC
ΔVCB
Problem 6.4Consider annpnSi-BJT at 300 K with the following parameters:
Nde =10^18 cm−^3
Nab =10^17 cm−^3
Ndc =5× 1016 cm−^3
Db =20.0cm^2 s−^1
Lb =15. 0 μm
De =10.0cm^2 s−^1
Le =5. 0 μm
emitter dimensions = 100μm× 100 μm
(a) Calculate the base width,Wb, that will allow a current gainβof 200 when the EBJ is
forward biased at 0.8 V and the BCJ is reverse biased at 5.0 V. Design the base width so
that the gain goal is achieved and the base resistance is minimum.
(b) Estimate the base resistance. Note that the base hole current flowssideways into the
device (figure 6.6). The hole mobility in the base is 300 cm^2 /V·s.
You may make the following approximations :
- The reverse bias collector current is zero.
- Wbis much smaller thanLb.
