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Unformatted text preview: M 43.9 6‘ 5.8
MED 4C9 SOLUTI ON 8 Name ECE Box # Average
Problem Score 1 223.5
2 20.4 Points
25 25 ECE4904 B2008 Semiconductor Devices Quiz 3 This is a closed book quiz! You are allowed one
81/2" X 11" sheet (both sides) of notes. Note: Potentially useful reference charts are given on
pages 7 and 8 (tear off to use if you like). Show all your work. Partial credit may be given. If
you think you need something that you can't remember, write down what you need and what you'd do if you
remembered it. Unless otherwise indicated, you may assume Si in
equilibrium at T=300K. Look for the simple, straightforward way to solve the problem for the level of accuracy required. Don't get
entangled in unnecessary algebra. As in real life, some problems may give you more
information than you need. Don't assume that all information must be used! It's your job to decide
what's relevant to the solution. You will have 25 minutes to complete this exam. There are 2 problems on a total of 8 pages. 1. An energy band diagram for a region of silicon semiconductor material is shown in the figure on the opposite page.
Assume T = 300K. a) Using the boxes in the figure, identify and label the
unlabeled energy levels on the diagram. [5] b) Do equilibrium conditions prevail? (Circle one): YES: EQUILIBRIUM NO: NONEQUILIBRIUM [1] EXPLAINI: [4] EF IS FLAT" c) Using the space in the figure, indicate which side is p—type
and which side is ntype [5] d) Is there a nonzero drift current anywhere in the material?
Nb... YES: Jdrm at o SOMEWHERE NO: Jdrm at o EVERYWHERE [1] EXPLAIN“ SEPARAT'ION OF CHARGE m DEPLEETION I41
REGION CRE’ATES a FIELD e) Is there a nonzero diffusion current anywhere in the
material? Jdm 1' O NO: Jdm 1: o EVERYWHERE [1} EXPLAIN“ CONCENTRATION GIQADIEMT: ‘41 Indicate ’
here for (c): n P E? NEAR Ec E; NEAR Ev
n—WPE p'TYPE The same energy band diagram from problem (1) is shown again
in the figure on the opposite page. Determine the built—in. voltage VM (accuracy' 2 significant
figures):
[5] b) NA: Pp: m'. Q Determine the doping density NA on the p—side and ND on the n—
side (accuracy 2 significant figures): NA = 2.2EH2 /CM3 (0.14 /o,ozs9) [5]
ND = 5.E1'é» /CM3 ND :nnzmeon/Mm) C) Using the space in the figure, sketch the extent of the
depletion region near the junction. Be sure your sketch
correctly indicates which side contains most of the depletion
region! [5] d) Using the axes in the figure,
Assume a step junction.
in the box indicated. sketch the doping profile.
Be sure to label the vertical axis [5] Using the axes in the figure, sketch the shape of the charge density p, the electric field 8, and the electrostatic
potential (voltage V). [5] DEPLETMN REGION I EXTENDS FURTHER
ere or (c). Axes for (d): Axes for (e): fonde V°C ‘ffdx ...
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 Fall '08
 MCNEILL

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