ECSE-2210 Microelectronics Technology
Fall 2003 Homework - 7
Due Date: October 21, 2003
Reading List: Chapter 10, Chapter 11 (pages 389 - 403)
1. Consider an npn transistor with doping concentration and dimensions shown below.
Answer the following questions.
a. If VBC = 0, and IC = 1 mA, what is value of VBE ?
b. With the transistor biased as in (a), what is the component of the base current due to
recombination in the base region?
c. With the transistor biased as in (a), what is the component of the base current due to
injection of holes into the emitter region?
d. What is the value of the emitter injection efficiency,
γ
?
e. What is the value of the base transport factor,
α
T ?
f. What is the value of the common emitter current gain,
β
dc ?
g. If VBE is held constant at the value found in (a), and the collector-to-base voltage is
increased so as to reduce the width of the neutral base region, WB , to 10-4 cm, what is
the common emitter current gain,
β
dc now? Note that this is called “base width
modulation” (also called “ Early effect”) which is common in narrow base-width
transistors.
Area A = 1 cm2
Emitter Base Collector
Doping conc. (cm-3) 5×1018 1016 5×1018
W (µm) 10 2 10
Lifetimes (s) 10-9 10-7 10-9
Elect. mobility (cm2/Vs) 120 1000 120
Hole mobility (cm2/Vs) 75 300 75
N P N
WE WBWC