pn JUNCTION DIODE

TEORI DASAR HUBUNGAN
SEMIKONDUKTOR
Hamzah Afandi, Antonius Irianto dan
Betty Savitri
Source: Millman, Jacob, Grabel, Arvin, Microelectronics,
Mc. Graw Hill Int. Ed., 1994.
Robert Boylestad, Louis Nashelsky
Sixth Edition; Prentice Hall,1997.
Review: Semiconductor Properties Variation
– Intrisic Concentration vs Temperature:
ni  A0T 
3  EG 0 / kT
2
– Mobility vs Temperature:
 m ; m =2.5, m =2.7 (100<T<400K)
n
p
 T
0
– Mobility vs Electric Field intensity:
 n  0 n
 nn  00nn
103 V/cm
1212
 n   0 n
104 V/cm
1
~ 107 cm/s
Review: Currents in semiconductor
• Drift Current:
J  q(n n  p p )  
  qn n  p p 
Drill:
Calculate the conductivity of an extrinsic semiconductor with
donor atom’s concentration of 1016 atom/cm3 (at 300K)!
 n  1500
 p  475
cm 2
cm 2
V .s
V .s
ni  1.45 x1010
REVIEW: The Physics of Electronics
Carrier’s Concentration in extrinsic Semiconductor
Mass-Action Law
pn = ni2
Charge Density should maintain electric neutrality of crystal
ND  p  NA  n
For n-type semiconductor, NA = 0; thus:
2
ni
n  ND ; p 
ND
2
For p-type semiconductor, ND = 0; thus:
ni
p  NA ; n 
NA
Review: Currents in semiconductor
Jp
• Diffusion Current:
Einstein Relationship
between D and 
Dp
p

Dn
n
 VT
kT
T
VT 

V
q 11600
Concentration
p(x0)
dp
dx
x0
p(x1)
x
x1
J p  - q Dp dp/dx
A/m
2
Dp = Diffusion Constant of Carrier
Review: Currents in semiconductor

• Total Current:
Jp
Concentration
p(x0)
dp
dx
x0
p(x1)
x1
x
J p  q p p - q Dp dp/dx (A/m )
2
J n  q n n  q Dn dn/dx (A/m )
2
Review: Graded
semiconductor
Jp = 0; in open circuited steady
state condition
V21
p1
p2
Concentration
p(x1)
p(x2)
dp
dx
J p  q p p - q D p dp/dx
x1
D p   pVT
x2
0  q p p - q pVT dp/dx
x2
1 dp
  VT
(V / m)
p dx
dV
1 dp

 VT
dx
p dx
p1
V21  VT ln
(V )
p2
x2
1
x dV  x VT p dp
1
1
x
pn JUNCTION DIODE
Hamzah Afandi, Antonius Irianto dan
Betty Savitri
Source: Millman, Jacob, Grabel, Arvin, Microelectronics,
Mc. Graw Hill Int. Ed., 1994.
Open Circuited Junction
neutral
neutral
Semiconductors
Semiconductors
Holes
p type
Electrons
n type
Open Circuited Junction
Junction Formation
Junction
p type
n type
Depletion Region
Space Charged Region
Open Circuited Junction
Junction Formation
Charge Density (V)
Wn
-Wp
p type
n type
Depletion Region
Space Charged Region
Open Circuited Junction
Junction Formation
v( x' )
E ( x)  
dx'

W p
x
Wn
-Wp
p type
Field Intensity ()
Depletion Region
Space Charged Region
n type
Open Circuited Junction
Junction Formation
x
V( x) 
 E ( x' )dx'
W p
Wn
-Wp
V=0
p type
Electrostatic Potential (V)
Depletion Region
Space Charged Region
n type
V0
Open Circuited Junction
Junction Formation
Potential Barrier of electrons(V)
Wn
-Wp
V=0
V0
p type
n type
Depletion Region
Space Charged Region
Closed Circuited Junction
Forward Biased pn Junction
p type
n type
Depletion Region
Space Charged Region
Closed Circuited Junction
Forward Biased pn Junction
p type
n type
Depletion Region
Space Charged Region
Closed Circuited Junction
Reverse Biased pn Junction
p type
n type
Depletion Region
Space Charged Region
Closed Circuited Junction
Reverse Biased pn Junction
p type
n type
Depletion Region
Space Charged Region
Closed Circuited Junction
Reverse Biased pn Junction
p type
n type
Depletion Region
Space Charged Region
VOLT-AMPERE CHARACTERISTIC

I D  I S 

VD
VT

1

(A)
 = 2 (Si)
 = 1.5 (Ge)
ID
-VZ
VD
V
IS (A Scale)
Breakdown
Cut-in
Offest
Turn-on
Diode Circuit Analysis:
Load-Line Concept
R
 VD 50mV 
I D  5.10 
1


7
+
VAA
ID
_
+
_
(A)
VD
100
ID
80
VAA /R
Solve for:
VAA = 3 V
R = 2 K
60
40
IDQ
20
Q
VD
0
-0.2
0
0.2
0.4
VDQ
0.6
VAA
0.8
CALCULATION
EXAMPLES
Given in class