Si/SiGe(C) Heterostructures
S. H. Huang
Dept. of E. E., NTU
OUTLINE
•
•
•
•
Introduction
Strain Effects
Device Performance
Fabrication technologies
Introduction
•The Si/SiGe:C heterostructures add the colorful
creativity in the monotonic Si world.
•The Si/SiGe heterojunction bipolar transistors have the
cutoff frequency of 300 GHz and maximum oscillation
frequency of 285GHz with carbon incorporation in the
base. (IBM)
Table I: The recent performance of electronic and optoelectronic devices based on SiGe technology.
The last column indicates the growth techniques to achieve the device quality material
Device
Figure of Merit
Growth Technique
Strained NMOSFET
Peak effective electron mobility 800 cm2/Vs [6]
relaxed buffer
Strained PMOSFET
Peak effective hole mobility 2700 cm2/Vs [5]
relaxed buffer
Npn-HBT
fT=210GHz [1], fmax=285GHz [2]
Pseudomorphic
Pnp-HBT
fT=59GHz at RT, fT=61GHz at 85K [12]
Pseudomorphic
Heterojunction
Phototransistors
1.47 A/W at 850 nm, bandwidth=1.25 GHz [13]
Pseudomorphic
n-MODFET
Gm=460ms/mm fT=76GHz fmax=107GHz at RT [14] Gm=730ms/mm
fT=105GHz fmax=170GHz at 50K
relaxed buffer
p-MODFET
Gm=300ms/mm fT=70GHz fmax=135GHz at RT[15]
relaxed buffer
n-RTD
P/V7.6 at RT [7], 2 at 4.2K [8]
relaxed buffer
p-RTD
P/V=1.8 at RT, 2.2 at 4.2K[9]
Pseudomorphic
Detector (IR)
1.3μm , 1.5μm[16]
quantum dots
Detector (LWIR)
Schottky barrier:λc=10μm[17]
Pseudomorphic
LED
1.3μm , 1.5μm at RT[18,19]
Pseudomorphic
：SiGe virture atoms
: Si atoms
The strained SiGe grown on (100) Si. The misfit dislocation is the
missing bond between Si and SiGe atoms.
threading dislocation
strained Si or Ge
relaxed SiGe
misfit dislocation
Si
The misfit dislocation and threading dislocation. The misfit dislocation is at the
Si/SiGe interface, and threading dislocation ends at the surface of the epilayers.
SiO 2
20 nm
Si cap
Ge
Si spacer
Ge
Si spacer
Ge
~6nm
~100nm
~2nm
Si buffer layer ~ 50nm
p-type Si substrate
(a)
(b)
(a) TEM photo of multi-layer Ge dots. The spacer
thickness is ~20nm. The SiO2 dots are also formed above
the Ge dots. (b) The strain field in Si layers.
Composite dots with fine structures such as Ge/Si/Ge composite dots
(a)
(b)
AFM picture of (a) composite dots and
(b) conventional dots. The composite dots has larger coverage area.
1
1.2
1.2
1.0
0.9
1.4
0.8
1.6
strained SiGe
0.7
0.6
0.5
0.0
0.2
0.4
0.6
Ge mole fraction
0.8
1.8
2
2.2
2.4
1.0
l ( mm )
Energy(eV)
relaxed SiGe
wave length
1.1
The bandgap of strained Si1-xGex on (001) Si substrate and relaxed band gap of
Si1-xGex alloys. The showdow areas indicate the optical communication
bandwidth of 1.3 and 1.5 mm.
2
Hole Mobility (cm /Vs)
400
16
-3
NA=10 cm
T=300K
300
200
Theoretical mobility
Experimental Data
100
0
0.00
0.05
0.10
0.15
0.20
Ge Mole Fraction
Theoretical values of the hole mobility in relaxed SiGe alloys at 300K and doping
concentration of NA=1016cm-3 with experimental results of Gaworzewski
in-plane
out-of-plane
2
Majority Hole Mobility(cm /Vs)
1000
15
-3
NA=10 cm
17
-3
NA=10 cm
18
-3
19
-3
NA=10 cm
100
0.0
NA=10 cm
0.1
0.2
0.3
0.4
Ge Mole Fraction
The in-plane and out-of-plane majority hole mobility of SiGe
strained alloys for different doping concentration.
out-of-plane
in-plane
2
Minority Electron Mobility (cm /Vs)
350
300
18
N =10 cm
-3
A
250
19
N =10 cm
-3
A
200
20
N =10 cm
-3
A
150
100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Ge Mole Fraction
In-plane and out-of-plane minority electron mobilities of SiGe
alloys at different doping level at 300K.
2500
(Hole mobility cm /Vs)
2200
2000
2
2
Electron mobility (cm /Vs)
2400
2000
1800
1600
1400
1200
1000
-1.5
1500
1000
500
-1.0
-0.5
0.0
Strain () (%)
0.5
1.0
1.5
-1.5
-1.0
-0.5
0.0
Strain () (%)
The in-plane electron and hole mobility of strained Si.
0.5
1.0
1.5
Mobility Enhancement Fctor
2.5
2.0
1.5
Electron[Takagi et al.]
Hole[Oberhuber et al.]
1.0
0
10
20
30
40
50
Substrate Ge content (%)
The calculated electron and hole mobility enhancement factor in
MOS inversion layers of strained Si.
5
4
10
10
Hole Mobility (cm /Vs)
2
2
Electron mobility (cm /Vs)
in-plane
3
10
in-plane
4
10
3
10
2
10
-5
-4
-3
-2
-1
0
1
2
3
-5
-4
-3
-2
Strain  
Electron and hole mobility in strained Ge.
-1
0
1
Strain (%)
2
3
4
5
H+ H+ H+ H+ H+ H+ H+
Si1-xGex
Wafer A
Si1-xGex
Wafer A
1). Hydr ogen
im pla nt a t ion
Wafer B
3). S plit t ing a nnea ling
Wafer A
Si1-xGex
Si1-xGex
Wafer B
Wafer B
2). Hydr ophilic bonding a t low
t em per a t ur e
4). P olis hing
Smart-cut and layer transfer process flow for making strained Si
on SiGe-on-insulator material.
Cross-section TEM picture of relaxed SiGe on SOI using the smart-cut method.
Si
Si
or
SiGe
Si
electron energy
ΔEG
Si
ΔVn
SiGe
VBE
ΔVp
n-emitter
p-base
VCB
Ec
n-colledtor
Ev
distance
Band diagram of typical SiGe HBT. In forward active region, the base-emitter
junction is forward-biased (VBE) and the base-collector junction reverse-biased (VCB)
Ec
Φp
Ev
lin. graded
SiGe profile
Compositionally graded Si1-xGex can build an
electrical field in the base of Si/SiGe HBTs.
Gate
(a)
Gate
+
n ploly Si
Source
SiO2
(b)
Drain
O
strained-Si
n+
Source
60-100 A
n+
+
n ploly Si
SiO2
Gradedbuffer
Relaxed Si1-yGey
y=0.05 to x
O
strained-Si
n+
60-100 A
n+
strained-Si
Relaxed Si1-xGex
Drain
O
130-200 A
0.25-0.6μm
1.5μm
Relaxed Si1-xGex
0.25-0.6μm
Gradedbuffer
Relaxed Si1-yGey
y=0.05 to x
1.5μm
Device structures for strained Si NMOSFETs with (a) Si on the surface,
(b) Si buried channel.
1600
W X L =21X90 mm
Strained-Si (Buried)
2
meff(cm /V.s)
1200
Strained-Si (Surface)
800
400
VDS=40mV
290K
0
0.0
0.1
Control-Si
0.2
0.3
0.4
0.5
0.6
Eeff(MV/cm)
Effective low-field mobility versus effective field for different NMOSFETs.
The surface channel strained-Si mobility shows a fairly constant mobility
enhancement compared with that of control-Si device, while the buried
strained-Si mobility peaks at low fields but decreases rapidly at higher fields.
2
Effective Electron mobility (cm /Vs)
Str. Si/ Relx. SiGe 13%
Str. Si/ Relx. SiGe 28%
Str. Si/ Str. SiGe 30%/ Relx. SiGe 13%
1000
800
600
400
110%
200
0
Control
Universal mobility
0
500
1000
1500
Effective Filed (KV/cm)
NMOSFET effective mobility vs vertical effective field.
120
2
Effective Hole mobility (cm /Vs)
140
100
80
60
40
20
Str. Si/Str. SiGe 13%
Str. Si/Str. SiGe 28%
Str. Si/Str. SiGe 30%/ Relx. SiGe 13%
Control
Universal mobility
0
100 200 300 400 500 600 700 800 900 10001100
Effective Filed (KV/cm)
PMOSFET effective mobility vs vertical effective field.
EV
"BC"Device
Epi Layer Structure
Str.Si/Str.SiGe/Rlx.SiGe
Gate Oxide
Strained Si 7nm
Strained SiGe 30% 15nm
Relaxed SiGe Buffer
Schematic diagram of a buried strained-SiGe PMOSFET. Most
current flow is in the strained SiGe channel.
Si-cap
Si Ge
1-x
Si-cap
Si-cap
x
Si Ge
1-x
x
n + doping
p+ doping
p + doping
Si1-xGex
Si spacer
Si1-xGex
spacer
spacer
Gechannel
relaxed Si1-xGex
buffer
Si-channel
Si1-xGex channel
relaxed Si1-xGex
buffer
Si buffer
Si-substrate
Si-substrate
Si-substrate
(b)
(c)
(a)
Typical layer sequences:
(a) NMODFETs with Si-channel on relaxed-SiGe buffer, (b) PMODFET with SiGe
channel and (c) PMODFET with Ge channel on relaxed-SiGe buffer.
Effective Mobolity (cm2/Vs)
IBM (A)
y=0.3
3
10
DC
x=1 y=0.7
IBM (B)
y=0.3
DC
x=1 y=0.7
CNET
x=1 y=0.7
IBM (B)
x=0.8 y=0.3
IBM (A)
x=0.8 y=0.3
2
10
Hole mobility
Electron mobility
0.1
1
Eeff (MV/cm)
Available experimental data [71-75] at 300K for effective electron and hole
mobility in MODFET. “A” denotes modulation doping above strained Si channel,
“B” denotes doping supply layer below strained silicon channel, x is the Ge fracion
in the channel, and y is Ge fraction in the buffer layers.
Absorption length(mm)
10
3
10
2
1550 nm
1300 nm
10
1
820 nm
10
10
0
-1
strained SiGe
10
-2
0.0
0.2
0.4
0.6
0.8
1.0
Ge mole fraction
The absorption length at 820, 1300, and 1550 nm vs Ge mole fraction. The absorp
decreases as the Ge mole fraction increases. For the large Ge fraction, the shado
indicate the uncertainty of the estimation.
Wetting layer 2 nm
Si cap 3 nm
Ge dot
Si spacer 50 nm
Active region
(×4)
Si buffer layer 50 nm
p-Si sub
The structure of 5-layer Ge quantum dot devices prepared by
UHV/CVD