ECE 875: Electronic Devices

1
ECE 875Electronic Devices

• Prof. Virginia Ayres
• Electrical Computer Engineering
• Michigan State University
• ayresv_at_msu.edu

2
Lecture 18, 19 Feb 14
Chp. 02 pn junction C-V curves About Pr.
2.02 Mixed linearly graded and abrupt pn
junction About Pr. 2.03 More about the Debye
length
VM Ayres, ECE875, S14
3
VM Ayres, ECE875, S14
4
Epitaxial layer layer grown in front n-layer
grown on the p substrate formed IN an n-type
epitaxial layer
As grown n-type epitaxial layer
p substrate
VM Ayres, ECE875, S14
5
depletion capacitance .formed IN an n-type
epitaxial layer means formation of a depletion
region WD WDp WDn
As grown n-type epitaxial layer
p substrate
VM Ayres, ECE875, S14
WDn ?
WDp 0.07 mm
6
Find the thickness of the depletion region WDn
formed in the n-type epitaxial layer
As grown n-type epitaxial layer
p substrate
VM Ayres, ECE875, S14
WDn ?
WDp 0.07 mm
7
Find the thickness of the depletion region WDn
formed in the n-type epitaxial layer Under which
bias condition?
Vext
Reverse -1 V
As grown n-type epitaxial layer
p substrate
Equilibrium 0 V
Forward 0.95 V
VM Ayres, ECE875, S14
WDn ?
WDp 0.07 mm
8
Find the thickness of the depletion region WDn
formed in the n-type epitaxial layer Under bias
condition Vrev -1 V, for which WD is biggest.
Given WDp-max 0.07 mm. Find WDn-max
Vext
Reverse -1 V
As grown n-type epitaxial layer
p substrate
Equilibrium 0 V
Forward 0.95 V
VM Ayres, ECE875, S14
WDn ?
WDp 0.07 mm
9
Two ways to finish use Method 01
VM Ayres, ECE875, S14
10
Use intercepti
VM Ayres, ECE875, S14
11
Use slope
VM Ayres, ECE875, S14
12
Watch out for Units
VM Ayres, ECE875, S14
13
VM Ayres, ECE875, S14
14
Lecture 18, 19 Feb 14
Chp. 02 pn junction C-V curves About Pr.
2.02 Mixed linearly graded and abrupt pn
junction About Pr. 2.03 More about the Debye
length
VM Ayres, ECE875, S14
15
VM Ayres, ECE875, S14
16
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
VM Ayres, ECE875, S14
17
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
2nd easiest to find
Easiest to find
VM Ayres, ECE875, S14
18
D
D
VM Ayres, ECE875, S14
19
Find E max as if
Solve for E m
VM Ayres, ECE875, S14
20
Next step
VM Ayres, ECE875, S14
21
Relation of E max to WDn as if
VM Ayres, ECE875, S14
Use E m. Solve for WDn
22
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
?
2nd easiest to find
Easiest to find
?
VM Ayres, ECE875, S14
23
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
Find potential drop on p-side using correct
yi(x) formula for linearly graded Find potential
drop on n-side using correct yi(x) formula for
linearly graded ybi potential drop on p-side
potential drop on n-side
?
?
VM Ayres, ECE875, S14
24
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
?
?
?
What do you expect the E (x) plot to look like?
VM Ayres, ECE875, S14
25
VM Ayres, ECE875, S14
26
For mixed type pn doping, find WD ybi E
max NA-(x) and ND(x) E (x)
?
?
?
What do you expect the doping(x) plot to look
like?
VM Ayres, ECE875, S14
27
VM Ayres, ECE875, S14
28
Lecture 18, 19 Feb 14
Chp. 02 pn junction C-V curves About Pr.
2.02 Mixed linearly graded and abrupt pn
junction About Pr. 2.03 More about the Debye
length
VM Ayres, ECE875, S14
29
Debye length pn example on spring 2012 Midterm
VM Ayres, ECE875, S14
30
Debye length pn example on spring 2012 Midterm
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
VM Ayres, ECE875, S14
31
Debye length pn example on spring 2012 Midterm
LD 41.2 nm
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
VM Ayres, ECE875, S14
32
Debye length LD ? pos-neg shielding length
Debye shielding
LD 41.2 nm
NA-
ND
NA-
ND
NA-
ND
NA-
ND
NA-
ND
VM Ayres, ECE875, S14
33
In Sze abrupt pn junction calculations for E (x)
and yi(x)
r ? Q/WDn Area ND Single type of charge.
This is outside LD.
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
NA-
ND
ND
ND
NA-
NA-
NA-
NA-
NA-
VM Ayres, ECE875, S14
34
Will see Debye shielding length LD again
Chp. 03 metal-semiconductor interface develops
special charge layer to achieve shielding Chp.
04 Chp. 06 metal-insulator-semiconductor
interface develops inversion layer (gate/channel
region in a transistor) during operation
VM Ayres, ECE875, S14
35
Will see Debye shielding length LD again
Chp. 04, Fig. 4
Inversion region e-s ? surface charge Qs formed
in a p-side
VM Ayres, ECE875, S14
36
Will see Debye shielding length LD again Chp.
04, fig.4
Where
VM Ayres, ECE875, S14