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ECE 440
Homework IV
Fall 2009
Print your name and netid legibly. Show all work leading to your answer clearly
and neatly. Staple multiple pages.
1.
A Si bar is 0.2 cm long and 200 µm
2
in crosssectional area. Find the current at 300
K with 10 V applied to (a) the Si bar is doped with 1x10
17
/cm
3
gallium and (b) the Si
bar is doped with 1x10
17
/cm
3
gallium and 2x10
17
/cm
3
arsenic. Refer to Fig. 323 or
the mobility chart posted online.) (c) The silicon sample is grounded at x=0 and
biased at +10 V at x=0.2 cm. Draw the corresponding energy band diagram for case
(a).
2.
How long does it take for an average electron to drift 0.2 mm donors under an elec
tric field of 100 V/cm for: (a) pure Si and (b) Si doped with 6x10
16
/cm
3
donors at an
electric field of 100 V/cm? Repeat if the electric field is change to 10
5
V/cm. Assume
that the electron effective mass m
n
*=0.26 m
o
.
3. Consider a silicon sample at 300 K. Assume that the electron concentration varies
linearly with distance. At x=0, the electron concentration is n(0). At x=10 µm, the
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 Spring '09
 Emelianov

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