Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!
Chapter 8 Exercise Solutions
L p
Ex 8.1
=
n po
n i% N a
(#.' × #& ) = 4.' ×#& =
D p τ po
=
( 8) ( ' × #&
)
−8
= $."%' × #&
−4
cm
%
#&
=
"
' ×#& #$
cm −"
n
=
p no
% i
=
N d
(#.' ×#& ) = #.#%' × #& %
#&
% × #&
4
#$
n po
c
%
V a V t
p no
n p ( − x p ) = n po ep
&.$'& = ( 4.' × #& " ) ep &.&%'( = ".') × #&
p n ( x n )
#4
V = p no ep a V t
= 8.(% × #&
#4
cm −"
− x p << N a and p n ( x n ) << N d
so lo+ inection applies. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Ex 8.2
(
= #.$ × #&
Dn
+
τ no −#(
#
D p
N d
τ po
J n ( − x p ) =
$
% ×#& −4
eDn n po Ln
$
4.'8"×#&
%
#$
cm −"
eV a ep kT − #
−"
#.&' × ep − # & . &%'(
− x p = #.%& A-cm eD p p no eV a J p ( x n ) = ep kT − # L p J n
%
4
$."%'×#&
%
8 ' ×#&
−8
Ex 8.3 *e ind
cm
cm −"
(#.8 ×#& ) =
= #.$% × #&
−4
#.&' × ep − # & . &%'( J p ( x n ) = &.#"%' A-cm
%
/he total current density is:
J T
= J n − x p + J p ( x n ) = #.%& + &.#"%'
J T
= #."" A-cm
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
=
N d
−4
#'
#(
%
=
8 ×#&
− ( ) ( 8) (#.$% ×#& − ) #.$ ×#& =
)(#.8 × #& )
# %#& %#& # × + −) #' #$ #& % ×#& 8 ×#& J s = "."& × #& −#8 A-cm
L n
$ %
−#( #.$ ×#& ( ) ( %#&) ( 4.&'×#& −4 ) =
*e have that
# = eni% N a
=
ni
cm −"
&.$'& = (#.#%' × #& 4 ) ep &.&%'(
J s
N a
(#.8 ×#& ) =
= 4.&' × #&
m −"
n p
=
n i%
%
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!! D nτ no
( %#& ) (#&
Ex 8.4 −)
)
= 4.'8" × #&
−"
0n the n1re2ion, or N d
= % ×#$ cm −
"
,
Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! µ n
≅ $&&& cm
%
# %&) # × + #' −8 #$ ' ×#& 8 ×#& % ×#& or J s = #.$)) ×#& −#) A-cm
-31s
J = eµ n N d Ε n or
(.8 ' ×#&
−8
%
J
Ε n =
e µ n N d
=
79
#.""%'
(#.$ ×#&−#( )( $&&&) ( % ×#$ )
= &.&$(4 3-cm 0n the p1re2ion, or N a
V bi
= 8 ×#' cm − , µ p ≅ "%& cm -31
( % ×#' )(8 ×#$ ) = ( &.&%'() ln (#.8 ×#& $ ) %
= #.#)4 3 #- % % ∈ s (V bi + V R ) N a + N d W = e N N a d
"
%
cm J = eµ p N a Ε p
or
%(#".#) (8.8' ×#& −#4 )(#.#)4 + ') = −#( #.$ ×#& Ε p =
J e µ p N a
=
#.""%'
(#.$ × #&
−#(
)( "%&) 8 × #&
#'
= ".%' 3-cm !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
% × #' + 8 × #$ × #' #$ ( % ×#& )(8 ×#& ) or W
= %.#4#× #&
−4
#- %
cm
Ex 8.5 rom Eample 8.', +e have
E g
− eV a % kT %
5et T %
E g
=
= "#& 6,
E g
− eV a# kT #
= "&& 6,
T #
= #.4% e3,
and V a# /hen
= #.&'& 3.
#.4% − V a % "#&
=
#.4% − #.&'&
eniW %τ &
(#.$ ×#& − )(#.8 ×#& )( %.#4#×#& − ) − %(' ×#& ) #(
=
"&&
+hich yields V a % = #.&")) 3 so or
=
J gen
7c
4
8
J gen
∆V = #.&")) − #.&'& = −&.%" 3 ∆V = −#%." m3 per #&° C increase
$
= $.#$$ × #& −#& A-cm
J gen J s
=
$.#$$ ×#&
−#&
#.$)) ×#&
−#)
%
= ".$8 ×#& )
in
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
temperature. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Ex 8.7
Ex 8.6
7a J s
# = eni% N a
(
= #.$ × #&
Dn τ n & −#(
+
#
D p
N d
τ p&
)(#.8 × #& ) $
%
I Sn
= (#&
−"
= A ⋅
eni
%
Dn
N a
τ no
− #.$ ×#& ( )(#.' ×#& ) )⋅ #(
#&
% ×#&
#'
or
I Sn
= #.%)" × #& −#" A
%
%' ' ×#&
−)
Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I Sp
= (#&
−"
= A ⋅
eni%
D p
N d
τ po
C d
− ) ⋅ (#.$ ×#& )(#.' ×#& ) #(
#&
%
8 ×#&
#$
#& #&
−)
So 7a
C d
=
or I Sp
= 4.' × #&
−#'
V = I S ep a V t
= (#."#8 × #&
−#"
−4
= %.%" × #&
C d
−)
=
#
'
%( &.&%'()
(
)
)(' ×#& ) ] = %.&( ×#& −8 = %&.( n
+ %.#'' × #&
or C d
[( ).$#) ×#& − )(#& − )
−"
−)
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
A
−"
Test Your Understandin Solutions
A
No+
79 r d
)( ' ×#& ) ] = %.&) ×#& −( = %.&) n −4
&.$#& = (#."#8 × #& −#" ) ep &.&%'(
79 I D
7a r d
)
79
&.''& ) ep &.&%'(
= %.% × #&
%( &.&%'()
or C d
[( ).'##×#& − )(#& − ) $
+ %.#%' × #&
= I Sn + I Sp = #."#8 ×#& −#" A
7a I D
#
(
A
/hen I S
# = [ I pOτ pO + I nOτ nO ] % V t
V t
=
I D
=
=
&.&%'( %.% × #& − 4
&.&%'( %.%" ×#&
−"
= ##8 Ω
= ##.$ Ω
TYU 8.1
n po
=
n i% N a
(#.8 ×#& ) = $.48 ×#& − = $
' × #&
%
'
#$
cm
−"
=
p no
n i% N d
(#.8 ×#& ) = $.48 ×#& − = $
' × #&
%
#'
4
cm
−"
or V a ( ma ) ,
*e ind
V a I pO = I Sp ep , V t V a I nO = I Sn ep V t
p n ( x n ) so that
V a
/hen 7a I pO
I nO 79 I pO
I nO *e ind
= ).'##× #&
−$
A
= %.#%' ×#& −4 A = ).$#) × #&
−'
V = p no ep a V t
A
= %.#''×#& −" A
p ( x ) ( &.#) N d = V t ln n n = V t ln p no p no
( &.#) (' ×#' ) = ( &.&%'() ln −4 $.48 ×#& or V a ( ma ) = #.&$) 3 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
TYU 8.2
Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! or I p = '.44 mA V a en i% D n ⋅ ep 7a I n = A ⋅ !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
N a
= (#&
−#( #& % ( )( #.$ ×#& #.' ×#& ) )⋅
−"
' ×#&
#$
%'
×
' ×#&
= A ⋅
79 I p
#&
eni
%
D p
N d
τ po
TYU 8.4
V a V t
V ⋅ ep a V t
− ( )(#.' ×#& ) #.$ ×#& )⋅ #(
−"
#&
7a J ≅ J s ep
J s
%
#×#&
#$
#&
×
−)
&.$%' ⋅ ep &.&%'(
= #.'4 × #& −4 A = &.#'4 mA
or I n
= (#&
V t
τ no
−)
or I p
= #.&( × #&
7c I Total
−4
−"
= %.#") × #&
V bi
= &.#'4 mA
=
N d
(#.' ×#& ) = %.%' ×#& = #&
#&
= (#& −" ) ⋅
%
−4
A-cm
#$
4
cm
(#.$ ×#& )(#&) ( %.%' ×#& ) −#(
% × #' + 8 × #$ × #' #$ % #& 8 #& × × ( )( )
% ×#&
#- %
4.8$' ×#& ' cm −
/hen
4
−4
%
( % ×#' )(8 ×#$ ) = ( &.&%'() ln (#.' ×#& ) %
=
&.$%' × ep &.&%'(
#& − )
%
/hen
I p
#&
%(##.) ) (8.8' ×#& −#4 )( &.)&$8 − &."') W = −#( #.$ ×#&
−"
%
*e ind
V ⋅ ep a V t
*e ind
p no
#&
= &.)&$8 3
No+
n i%
τ po
)(#.' × #& )
A
TYU 8.3
W n
N d
&."' &.&%'(
79
= A ⋅
D p
J ≅ ( %.8(#× #& −#& ) ep
−"
or I Total = #.%4 mA !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I p
#
/hen
= #.%4 × #&
eD p p no
−#(
+
# %' # × + −) #' #& 8 × #& #$ % × #& J s = %.8(#×#& −#& A-cm
A = #.&( mA
+ #.&8) × #&
rom /;< 8.%, I n
τ no
(
= I n + I p
= #.'"8 × #&
Dn
= #.$ × #&
&.$%' ⋅ ep &.&%'( −"
# = eni% N a
J rec
=
eni W %τ o
V a % V t
ep
Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
=
(#.$ ×#& )(#.' ×#& )(4.8$'×#& ) − %(#& ) −#(
−'
#& )
&."' × ep %( &.&%'() J rec = '.&%& ×#& −4 A-cm J rec
7c
J
=
'.&%& ×#& −4 %.#") ×#& − 4
I nO
*e ind 7a I pO
%
I nO
= %."'
79 I pO
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I nO No+
TYU 8.5
= A ⋅
I Sn
= (#&
V = I Sp ep a , V t V = I Sn ep a V t
I pO
−"
eni
%
Dn
N a
τ no
−$
A
= (.)#×#& −' A = %.#") × #& −' A = #.)') ×#& −" A
# = [ I pOτ pO + I nOτ nO ] % V t
C d So 7a
− ) ⋅ (#.$ ×#& )(#.8 ×#& ) #(
$
%
%&)
% ×#&
' ×#&
#'
C d
−)
= '.%)4 ×#& −%# A
or I Sn
= #.#8#× #&
=
#
[(#.#8#×#& − )(#& − ) $
%( &.&%'()
)
)( ' × #& ) ] = &.(4& n = (.4& × #&
(
+ (.)# × #&
−'
−)
−#&
= A ⋅
I Sp
= (#&
−"
eni%
D p
N d
τ po
79
C d
− ) ⋅ (#.$ ×#& )(#.8 ×#& ) #(
%
8 ×#&
#$
= $.4#' × #&
or I Sp So I S
$
−%"
−)
A
#
+ #.)') × #&
[( %.#") ×#& − )(#& − ) '
%( &.&%'( )
(
(.8 #&
=
−"
)
)( ' × #& ) ] −)
−8
= #).& n !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! = #.)& × #&
= I Sn + I Sp = '.""8 ×#& −%# A &.()& = '.""8 ×#& − %# ep &.&%'(
7a I D
= (.8" × #&
−'
A
#.&4' = '.""8 ×#& − %# ep &.&%'(
79 I D
= #.)8 × #&
−"
TYU 8.6
rom i2ure '.", or N d
A
7a r d
=
79 r d
=
I D
=
&.&%'( (.8%8 ×#& − '
&.&%'( #.))( ×#&
−"
"
⇒ µ n ≅ (&& cm -31s #' or N a = % ×#& cm − ⇒ µ p ≅ 48& cm -31s
,
%
No+
V t
= 8 ×#$ cm −
= %$4 Ω
"
%
0n the n1re2ion, σ ≅ e µ n N d
= #4.$ Ω
(
= #.$ × #&
*e have
−#(
)( (&&) (8 ×#& ) #$
= ##.'% 7 Ω 1cm −
#
/hen
,
Semiconductor Physics and Devices: Basic Principles, 4 th edition Chapter 8 By D. A. Neamen Eercise Solutions !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
R n
=
l
( &.) = &.8$8 Ω (##.'%) (#& −" )
=
σ A
0n the p1re2ion, σ ≅ e µ p N a
(
= #.$ × #&
−#(
)( 48&) ( % ×#& ) #'
= &.#'"$ 7 Ω 1cm
−#
/hen
l
=
R p
σ A
( &.) = $'.# Ω ( &.#'"$) (#& − " )
=
/he total resistance is R = Rn + R p = $$ Ω !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! TYU 8.7
t s
7a er
τ pO
I F
=
I F
+ I R
No+
I R
≅
V R R R
=
% 4
= &.' mA
So
er
t s τ pO
=
rom Appendi =,
#.)' #.)' + &.'
t s τ pO
= &.))8
≅ &.8$4
So that
t s
= ( &.8$4) % (#& −) ) = &.)4$ × #& −) s
79
er
t % τ pO
+
ep ( − t %
τ pO
π t % τ pO
)
I = # + ( &.#) R I F
&.' = # + ( &.#) = #.&%8$ #.)' By trial and error t % ≅ #.%' τ pO
⇒ t % = (#.%') (#& −) ) = #.%'×#& −) s !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!