YOUR NAME_______________________________
Department of Electrical Engineering and Computer Science
Massachusetts Institute of Technology
6.012 Electronic Devices and Circuits
Exam No. 2
Notes:
1. Unless otherwise indicated, assume room temperature and that kT/q is 0.025 V.
You
may also approximate [(kT/q) ln 10] as 0.06 V.
2. Open book; 6.012 text and any other notes permitted.
3. All of your answers and any relevant work must appear on these pages. Any
additional paper you hand in will not be graded.
4. Make reasonable approximations and assumptions. State and justify any such
assumptions and approximations you do make.
5. Be careful to include the correct units with your answers when appropriate.
6. Be certain that you have all nine (9) pages of this exam booklet and make certain that
you write your name at the top of this page in the space provided.
6.012 Staff Use Only
PROBLEM 1
(36 maxium)
PROBLEM 2
(28 maxium)
PROBLEM 3
(36 maxium)
TOTAL
(100 maxium)
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Page 2 of 9
Problem 1
(36 points)
This problem concerns the pn junction diode illustrated below; it is not a silicon
diode. Throughout this device , the minority carrier lifetime,
min
, is 10
7
s; the electron
mobility, µ
e
, is 3,600 cm
2
/Vs; the hole mobility, µ
h
, is 256 cm
2
/Vs; and the intrinsic
carrier concentration at room temperature, n
i
(300K), is 10
5
cm
3
. The doping level on
the pside of the junction, N
Ap
, is 10
17
cm
3
and on the nside, N
Dn
, it is 10
16
cm
3
. The
crosssectional area of the junction is 10
4
cm
2
.
n
10 cm
16
3
p
10 cm
17
3
A
B
+

v
AB
i
D
x (µm)
5
0
5
10
15
20
25
a)
What are the relative magnitudes of the hole and electron currents at x = 0 when
this device is forward biased? You may use the short base or long base approximation,
which ever is appropriate, on either side of the junction (i.e., you should not have to use
the complete sinh and cosh expressions).
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 Fall '03
 Prof.CliftonFonstadJr.
 Transistor, Pn junction, bias point

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