SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

7.4. BIPOLAR JUNCTION TRANSISTORS: A CHARGE-CONTROL ANALYSIS 321

VCC

RCC

C vout

B

vin

E

(a)

(b)

n+ - E p - B n- - C

- ΔQBE +ΔQBE +ΔQBC BC

- ΔQF

(c)

n+ - E p - B n- - C

iB

iE iC

n+

n+

wB wd,BC

−ΔQ'

Figure 7.7: Charge control model for forward active mode. (a) Bipolar transistor biased in
common emitter configuration. (b) Charge components corresponding to a change in base-
emitter voltageΔVBE. Because of charge injection into the base-collector depletion region,
ΔQBC=ΔQ

′

BC(c) Currents at each of the three transistor terminals.