semiconductor device modeling and characterization ee5342, lecture 5-spring 2003
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Semiconductor Device Modeling and Characterization EE5342, Lecture 5-Spring 2003. Professor Ronald L. Carter [email protected] http://www.uta.edu/ronc/. First Assignment. Send e-mail to [email protected] On the subject line, put “5342 e-mail” In the body of message include - PowerPoint PPT PresentationTRANSCRIPT
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Semiconductor Device Modeling and CharacterizationEE5342, Lecture 5-Spring 2003
Professor Ronald L. [email protected]
http://www.uta.edu/ronc/
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First Assignment
• Send e-mail to [email protected]– On the subject line, put “5342 e-mail”– In the body of message include
• email address: ______________________• Last Name*: _______________________• First Name*: _______________________• Last four digits of your Student ID: _____
* As it appears in the UTA Record - no more, no less
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S-R-H net recom-bination rate, U• In the special case where no = po
= o = (Ntvtho)-1 the net rec. rate, U is
)pn( ,ppp and ,nnn where
kTEfiE
coshn2np
npnU
dtpd
dtnd
GRU
oo
oT
i
2i
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S-R-H rec forexcess min carr• For n-type low-level injection and net
excess minority carriers, (i.e., no > n = p > po = ni
2/no),
U = p/o, (prop to exc min carr)
• For p-type low-level injection and net excess minority carriers, (i.e., po > n = p > no = ni
2/po),
U = n/o, (prop to exc min carr)
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Minority hole lifetimes. Taken from Shur3, (p.101).
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Minority electron lifetimes. Taken from Shur3, (p.101).
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Parameter example
• min = (45 sec) 1+(7.7E-18cm3Ni+(4.5E-36cm6Ni
2
• For Nd = 1E17cm3, p = 25 sec
– Why Nd and p ?
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Direct rec forexcess min carr• Define low-level injection as
n = p < no, for n-type, andn = p < po, for p-type
• The recombination rates then areR’n = R’p = n(t)/n0, for p-type,
and R’n = R’p = p(t)/p0, for n-type
• Where n0 and p0 are the minority-carrier lifetimes
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S-R-H rec fordeficient min carr• If n < ni and p < pi, then the S-R-H net
recomb rate becomes (p < po, n < no):
U = R - G = - ni/(20cosh[(ET-Efi)/kT])
• And with the substitution that the gen lifetime, g = 20cosh[(ET-Efi)/kT], and net gen rate U = R - G = - ni/g
• The intrinsic concentration drives the return to equilibrium
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The ContinuityEquation• The chain rule for the total time
derivative dn/dt (the net generation rate of electrons) gives
n,kz
jy
ix
n
is gradient the of definition The
.dtdz
zn
dtdy
yn
dtdx
xn
tn
dtdn
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The ContinuityEquation (cont.)
vntn
dtdn then
,BABABABA Since
.kdtdz
jdtdy
idtdx
v
is velocity vector the of definition The
zzyyxx
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The ContinuityEquation (cont.)
etc. ,0xx
dtd
dtdx
x
since ,0dtdz
zdtdy
ydtdx
xv
RHS, the on term second the gConsiderin
.vnvnvn as
ddistribute be can operator gradient The
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The ContinuityEquation (cont.)
.Equations" Continuity" the are
Jq1
tp
dtdp and ,J
q1
tn
dtdn
So .Jq1
tn
vntn
dtdn
have we ,vqnJ since ly,Consequent
pn
n
n
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The ContinuityEquation (cont.)
z).y,(x, at p
or n of Change of Rate Local explicit"" the
is ,tp
or tn
RHS, the on term first The
z).y,(x, space in point particular a at p or
n of Rate Generation Net the represents
Eq. Continuity the of -V,dtdp or
dtdn LHS, The
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The ContinuityEquation (cont.)
q).( holes and (-q) electrons for signs
in difference the Note z).y,(x, point
the of" out" flowing ionsconcentrat
p or n of rate local the is Jq1
or
Jq1
RHS, the on term second The
p
n
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The ContinuityEquation (cont.)
inflow of rate rate generation net
change of rate Local
:as dinterprete be can Which
Jq1
dtdp
tp
:as holes the for equation
continuity the write-re can we So,
p
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Poisson’sEquation• The electric field at (x,y,z) is
related to the charge density =q(Nd-Na-p-n) by the Poisson Equation:
silicon for 7.11
andFd/cm, ,14E85.8
with , ypermitivit the is
xE
E where, ,E
r
o
ro
x
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Poisson’sEquation• For n-type material, N = (Nd - Na) >
0, no = N, and (Nd-Na+p-n)=-n +p +ni
2/N
• For p-type material, N = (Nd - Na) < 0, po = -N, and (Nd-Na+p-n) = p-n-ni
2/N
• So neglecting ni2/N, [=(Nd-Na+p-n)]
carriers. excess with material type-p
and type-n for ,npq
E
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Quasi-FermiEnergy
used. be must level
Fermi-quasi the then ,nnn i.e.,
m,equilibriu not in ionconcentrat the If
kT
EEexp
nn and ,
nn
lnkTEE
:by given are level Energy Fermi the and
conc carrier mequilibriu the m,equilibriu In
o
fif
i
o
i
ofif
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Quasi-FermiEnergy (cont.)
kT
EE
nnn
nnn
kTEE
fifn
i
o
i
ofifn
exp
:is density carrier the and
, ln
:defined is (Imref) level Fermi-Quasi The
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Quasi-FermiEnergy (cont.)
kT
EE
npp
npp
kTEE
fpfi
i
o
i
ofpfi
exp
:is density carrier the and
, ln
:as defined is
(Imref) level Fermi-Quasi the holes, For
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Energy bands forp- and n-type s/c
p-type
Ec
Ev
EFi
EFp
qp= kT ln(ni/Na)
Ev
Ec
EFi
EFnqn= kT ln(Nd/ni)
n-type
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JunctionC (cont.)
xn
x-xp
-xpc xnc
+qNd
-qNa
+Qn’=qNdxn
Qp’=-qNaxp
Charge neutrality => Qp’ + Qn’ = 0,
=> Naxp =
Ndxn
Qn’=qNdxn
Qp’=-qNaxp
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JunctionC (cont.)• The C-V relationship simplifies to
][Fd/cm ,NNV2
NqN'C herew
equation model a ,VV
1'C'C
2
dabi
da0j
21
bi
a0jj
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JunctionC (cont.)• If one plots [C’j]
-2 vs. Va
Slope = -[(C’j0)2Vbi]-1
vertical axis intercept = [C’j0]-2 horizontal axis intercept = Vbi
C’j-2
Vbi
Va
C’j0-2
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Arbitrary dopingprofile• If the net donor conc, N = N(x), then at xn,
the extra charge put into the DR when Va->Va+Va is Q’=-qN(xn)xn
• The increase in field, Ex =-(qN/)xn, by Gauss’ Law (at xn, but also const).
• So Va=-(xn+xp)Ex= (W/) Q’
• Further, since N(xn)xn = N(xp)xp gives, the dC/dxn as ...
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Arbitrary dopingprofile (cont.)
p
n3j
nn
p
n2j
n
p2n
xNxN
1
dVdC
q
'C
dCVd
qC
dxCd
N with
,dVCd
dCxd
qNdVxd
qNdVdQ
C further
,xN
xN1
'C
dx
dx1
WdxdC
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Arbitrary dopingprofile (cont.)
,VV2
qN'C where , junctionstep
sided-one to apply Now .
dVdC
q
'C xN
profile doping the ,xN xN orF
abij
3j
n
pn
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Arbitrary dopingprofile (cont.)
bi0j
bi
23
bi
a0j
23
bi
a30j
V2qN
'C when ,N
V1
VV
121
'qC
VV
1'C
N so
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Example
• An assymetrical p+ n junction has a lightly doped concentration of 1E16 and with p+ = 1E18. What is W(V=0)?
Vbi=0.816 V, Neff=9.9E15, W=0.33m• What is C’j? = 31.9 nFd/cm2
• What is LD? = 0.04 m
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Law of the junction(follow the min. carr.)
t
bia
n
p
p
na
t
bi
no
po
po
no
po
not
no
pot2
i
datbi
V
V-Vexp
n
n
pp
,0V when and
,V
V-exp
n
n
pp
get to Invert
.nn
lnVp
plnV
n
NNlnVV
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Law of the junction (cont.)
dnonapop
ppnn
ppopppop
nnonnnon
a
Nnn and Npp
injection level- low Assume
.pn and pn Assume
.ppp ,nnn and
,nnn ,ppp So
. 0V for nnot' eq.-non to Switched
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Law of the junction (cont.)
t
a
pt
a
n
t
a
t
a
t
bi
t
bia
VV
2ixpp
VV
2ixnn
VV
no
2iV
V
pono
pon
VV
nopoVV-V
pn
ennp also ,ennp
Junction the of Law the
enn
epn
np have We
enn nda epp for So
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pt
apop
nt
anon
V
V-
pononoV
V-V
pon
t
biaponno
xx at ,1VV
expnn sim.
xx at ,1VV
exppp so
,epp ,pepp
giving V
V-Vexpppp
t
bi
t
bia
InjectionConditions
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Ideal JunctionTheory
Assumptions
• Ex = 0 in the chg neutral reg. (CNR)
• MB statistics are applicable• Neglect gen/rec in depl reg (DR)• Low level injections apply so that np < ppo for -xpc < x < -xp, and pn < nno for xn < x < xnc
• Steady State conditions
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Ideal JunctionTheory (cont.)
Apply the Continuity Eqn in CNR
ncnn
ppcp
xxx ,Jq1
dtdn
tn
0
and
xxx- ,Jq1
dtdp
tp
0
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Ideal JunctionTheory (cont.)
ppc
nn
p2p
2
ncnpp
n2n
2
ppx
nnxx
xxx- for ,0D
n
dx
nd
and ,xxx for ,0D
p
dx
pd
giving dxdp
qDJ and
dxdn
qDJ CNR, the in 0E Since
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Ideal JunctionTheory (cont.)
)contacts( ,0xnxp and
,1en
xn
pxp
B.C. with
.xxx- ,DeCexn
xxx ,BeAexp
So .D L and D L Define
pcpncn
VV
po
pp
no
nn
ppcL
xL
x
p
ncnL
xL
x
n
pp2pnn
2n
ta
nn
pp
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Excess minoritycarrier distr fctn
1eLWsinh
Lxxsinhnxn
,xxW ,xxx- for and
1eLWsinh
Lxxsinhpxp
,xxW ,xxx For
ta
ta
VV
np
npcpop
ppcpppc
VV
pn
pncnon
nncnncn
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References
• 1Device Electronics for Integrated Circuits, 2 ed., by Muller and Kamins, Wiley, New York, 1986.
• 2Physics of Semiconductor Devices, by S. M. Sze, Wiley, New York, 1981.
• 3 Physics of Semiconductor Devices, Shur, Prentice-Hall, 1990.