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Unformatted text preview: You must provide your name on the answer sheet. In addition, you are asked to voluntarily “provide” your social
security number in order to verify your identity and avoid confusion between “two students“ with the same name.
Your social security number is sought for identiﬁcation purposes pursuant to Public Law 93—579 and is being used
as part of a system of "student" records that has been in effect prior to 1970. If you do not want to provide your
social security number, you must write on the answer form an alternative identiﬁer. [An alternative choice “would
be” the University ‘NetID’ (network identiﬁcation name) or the 9digit blue number on each person's I—card]. ECE 440 H Spring 2006 Name sal’n
Net ID# Section ECE 440  EXAM N0. 1
Thursday February 23, 2006
7:008:30 p.m. ROOM ASSIGNMENTS
Room 100 MSEB
K.C. Hsieh Section C, J. Tucker, Section E, S. Bishop Sections X and G Conﬂict Exam #1 — Thursday, Feb. 23, 2006, 4:005:30 p.111.
Room 245 Everitt Lab. NOTE: This is a closed book and closed notes exam. Unless stated otherwise, do
your work on the page of the problem and if necessary on the preceding blank page. It is mandatory that proper units be included exglicitly along with
the numerical value for each term in a quantitative calculation, showing how the units of the ﬁnal answers are derived. Failure to do this will result in an
credit. Circle our answer. Be neat! For each roblem ou must show complete work and indicate your reasoning. No credit will be given if you do not Show the complete work
and describe our racednre even if the answer is correct. Write your name,
ID#, and section on this page and Sign below. Signature: Your Exam Score: l. A silicon sample is doped with 8x1014 Sb atoms/cm3. The donor level is 59 meV away from
the conduction band edge, i.e. ECED=5 9 meV. (a) (10 points) Determine the electron and hole concentrations at 300 K under equilibrium
conditions, and sketch 3 energy band diagram. Label clearly EC, EV, EF, and Bi. Assuming that 131 coincides with the center of the band gap, and the band gap energy is 1.1 eV at 300 K. N >>n MAX 360k on Wm adfwfw'ﬁw Layer
a N
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n°=n‘Wf——:';}"_‘ “L (b) Assume that the F ermi—Dirac statistics applies to electrons in energy bands as well as with
impurities. At temperature Th, half of the antimony atoms are ionized. Answer the following questions.
(bl) (4 points) Is Th higher or lower than 300 K and why? . ‘~ . . 1 at l'kMW'CS lMm
. Wwﬁ tau $6!» twfmd'scL
I2 szVKS a): 300K mosr shun” atonws chmJ4” “gave” Mmdmsldlew”
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Label ciearly EC, EV, ED, BF, and E1. Assuming that E coincides with the center of the band gap, and the band gap energy increases to 1.12 eV at temperature Th. n __L —'  “: U  b 
aw “i “W “WEE?” z p t
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at?» ...__ _______, E". (b3) (6 points) Estimate the physical number of this particular temperature Th. Assume that
. . . . . _ 18
the intrinsic carrier concentration ni : JNCNV exp(—Eg /2kT)72.31xlO exp(Eg/2kT). v (1:111, nurde=¢xioZ§ M Ewe: EF “'54:
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” gush/MAI [sunk = :HOK __——‘—' «tameraw =r Th: asamw 2. A small Si bar at 300 K is uniformly doped with phosphorous to a density of 6‘211016/0m3 as
sketched below. L=O.1 cm (a) (7 points) Determine the average drift velocity Vx of the carriers (including sign) in Gin/5.. plan
a. 4L
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1 V)f .jAns 3‘ vs Macaw s (b) (5 points) Use your result in part (a) to calculate the current density (Afomz) inside the
bar. ‘ (c) (7 points) Calculate the conductivity of the bar and its resistance for a cross—sectional area
of (100 pm) 2. 6:ZHDMH : IMHO—15c. icxiokbcmdic 3w =16? elm)" I = A6'{~ : (Ivoxlo‘l‘om )2 X 153%?“ r mo it = 7.6?Ma2Aﬂ R: _V_ =_13_‘L~——— * 3°“ : 7.58xio‘1Ar (d) (6 points) If a second ddping with boron at 3x1016/Cm3 is added to the initial phOSphorous doping of 6x1016/cm3, how would the following quantities be affected
(higher or lower) and Why? . . 15
Gamer densrryz LOW heme hoeup—NA = 3:004; 16
Mobility: LOW 19me 85 wave Cﬂkfllwwcﬁ) it‘d/WW9»; (“4*N4:$x‘°/‘:f) '13 “MIR mob: EU I. dWl
Resistance: Hljkw bcww. r?) be?!» éawq uww A silicon sample that is uniformly doped with 1 x 1016 /crn3 As atoms is continuously
illuminated (steady state) with light that generates a spatially uniform concentration of electron hole pairs (BIIF) An = Ap = 4 x 1014 cm‘3. Assume that In = 'cp r— 5 tts and that T:
300K. (a) (2 points) Determine the optical generation rate gop (form—s) during the steadystate
illumination. Fw cm n—‘t‘fyu, SayWPLL , Mics wt. 11M w‘wwH} wn‘ws. H:
AF =¢x1023 << thlxwéj) So Lcw«iuwe WW‘M lwlats 4F 4310iq‘4w3 9 l?
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.4? go? 1? =3) 80f I} ﬂ‘o'bSM W34“ (b) (4 points) Determine no , p0 , and the total steady—state concentrations of electrons (a) and
holes in the sample. lb . .
m and = lxw C.’ Nd »"l)
” °‘ 43 10 9
= n“ = AUX"? 2 2.25m:
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P [Jo+5?“ P. P /3 (c) (4 points) Calculate the resulting steady—state positions of the quasi—Fermi levels relative
to E; , that is, F”  El and 15 — Fp. n Fn‘EC
Pt= :wf’ ‘
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positions of the quasi—Fermi levels relative to El (assume E; is located at mid—gap). (6) Assume that at a point in time (t = 0) the steady—state illumination ceases abruptly, and
the excess carrier concentrations begin to decay (recombine). (cl) (5 points) Determine sufﬁcient data points to plot the decay of n(t) and p(t) as a
function of time from t = 0 to 20 us on the empty graph provided, (e2) (6 points) Referring to part (b) above, mark and label the positions of the steadystate
concentrations of the majority carriers and minority carriers at t = 0, and indicate the
contributions of the photoaexcited EHP, An and Ap, to these total, steady—state concentrations.  t 
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explanations. Toss—Q2. "—QSS'W
{r 0.15 8V 0.2 EV O 0.5 cm 1.5 cm (a) (4 points) Determine the net current through the sample. The not WYM “‘0 W bwsem SWQ L}, M WM“: tﬁwhalleIMm. (b) (6 points) What is the direction and magnitude of the electric field at x = 0.5 cm? I aEL’tiv'
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EL'EF : (5):”; WP( 0" ) ‘3l3x16?3
Pf“ W? k 0.02:1 0M
2. 3
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