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Aspects of Si-Ge heteroepitaxial system
Tonkikh Alexander
Max-Planck Institute of Microstructure Physics
Dr. Peter Werner - head of the group, TEM analysis
Dr. Nikolay Zakharov - TEM analysis
Dr. Vadim Talalaev - PL analysis
Ph.D. student Luise Schubert - growth assistance
Gerhard Gerth - technical support, growth assistance
Andreas Frommfeld - technical support, growth assistance
Ioffe Physical-Technical Institute
Dr.hab. George E. Cirlin
Dr.hab. Vladimir G.Dubrovskii
Dr.Vyacheslav A.Egorov
Prof.Dr.hab. Viktor M.Ustinov
Coffee seminar 03 of December 2003
Outlook
Ioffe Institute presentation
Brief introduction into Si-Ge MBE technique
Ge islands on a Si (100) surface
Kinetics of the islands formation
Abnormal Sb impact
Si-Ge multilayer structure
Band structure
Multilayer structure properties
Au impact
Conclusion
Ioffe Physical-Technical Institute
194021 Politechnicheskaya 26, Saint-Petersburg, Russia
http://www.ioffe.rssi.ru
Founded in 1918 by
Abram Fedorovich Ioffe.
Ioffe-effect
hole conductivity conception
The main old building during winter time.
Scientific adviser:
Nobel-prize winner
Zhores I. Alferov*
*Double heterostructure laser inventor
The most famous scientists:
Ya.I.Frenkel Exc. Pred., Kinet. of Liq.
N.N.Semenov Chain chemical reactions
P.L.Kapitsa super fluidity effect
L.D.Landau Q.theory of el. diamagn.
I.V.Kurchatov Sc. Adv. of NWP
Institute departments
Center of Nanoheterostructure Physics
Division of Solid State Electronics
Division of Solid State Physics
Division of Plasma Physics, Atomic Physics and Astrophysics
Division of Physics of Dielectric and Semiconductors
Educational Center
Physics of Semiconductor
Head: Zh.I. Alferov
Heterostructures Laboratory
Research activities:
http://www.ioffe.rssi.ru/sem_tech/
Deputy Head:
Nikolai N. Ledentsov
* physics and technology (MBE, MOCVD) of silicon and III-V
semiconductor heterostructures (quantum wells, quantum dots)
* electron materials science and characterization
* optoelectronics, nanoelectronics (low-dimensional heterostructures)
* semiconductor laser diodes, photodetectors,
power and high speed semiconductor devices
* postgrowth processing of semiconductors devices
Deputy Head:
Victor M. Ustinov
Silicon MBE
Principle of operation
Tsub
Si substrate
TSi
Si source
Real setup Riber Siva-45
TGe
Ge source
MBE conditions:
HV/UHV P<10-6torr
Tsub<Tsi and Tge
in situ control
P~10-9torr
in situ control: RHEED, QMS
Si-Ge heteroepitaxial system
Metastable epitaxial layer against islanding and misfit dislocation formation
Ge bulk
Ge epilayer
Island formation
y
Si bulk (substrate)
Both diamond
(face-centered cubic)
like structure
aSi=5.431Å
aGe=5.658Å
x Si substrate
dGe < 4ML
axGe=aSi
ayGe>aGe
Stranski-Krastanow
growth mode
Ge islands on a Ge
wetting layer
Δ= 2(aGe- aSi)/(aGe + aSi)x100%=4%
In situ observation of the island formation
Reflection High Energy
Electron Diffraction system
(RHEED)
Surface with Ge islands
Start (p=0)
P1 (p=40)
P0 (p=60-80)
P2 (p=110)
Finish (p=198)
Ee~30KeV, λe = h/(2meEee) ~ 0.1Å
 ~ 1-4°

substrate
dGe=7Å
screen
Flat 2x1 reconstruction of Si(100) surface
The dynamic of RHEED pattern intensity
on a white section
d=0ML
d=3.4A
d=4.2A
d=6.3A
d=6.5A
d=6.6A
d=6.8A
d=7A
90
2D-3D
transition
at 6.8Å
(=4.8ML)
of Ge!
dGe=0Å
Spot Intensity, %
E-gun

80
70
60
50
40
30
20
10
P0
P1
P2
0
0
20
40
60
80
100
120
140
Position, pixel
160
180
200
Ex situ observation of the Ge on Si islands
Bimodal island
shape distribution
Atomic force microscopy
(tapping mode)
5.5Å Ge
RHEED
N=3.1x108cm-2
8.5Å Ge
AFM
RHEED
N=3.3x1010cm-2
huts <105>
huts+domes
Tsub=500°C
Islands height, nm
AFM
Tsub=550°C
11.0
10.5
10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
440
domes
Tsub=600°C
Phase diagram
for Ge islands
on Si (100)
surface
Domes
Huts
460
480
500
520
540
560
580
0
Substrate temperature, C
600
Kinetics of Ge islands formation*
Free energy of coherent island formation:
Ge island
F (i)  Felas  Fsurf  Fattr
Felas  1  z ( )  02l02 h0i  0
Fsurf 

Fattr 
0
h
 exp(
)  l02 h0i
h0
k0 h0
 ( )
cos( )


Ge WL
h
Si
L
  (0)  L  0
2
The main growth mechanism is the diffusion of the
atoms from the wetting layer to the islands with D(T).
The parameters of the system after the relaxation stage:
Equation of material balance:

t
3
2
heq  h0  dt V (t )  h  h l  d g (  , t )
/
/
0
2
0 0
0
g(,t) - island size distribution
g(,0)=0,
i=2/3
-new variable
V(t) - growth rate
  2 Te 1/ 2 
 
hc  heq 1  
5
T
ln
Q
 
 
4
T  ln Q 

N  2 heq 
Te  Q 
l0
Q
D(T )
VT
3/ 2
 3 2 (H  h ) T

LR   l0 d 0 0 eq e cot an 
heq
T
2

1/ 3
1/ 2
 Q 


 ln Q 
* V.G.Dubrovskii, G.E.Cirlin and V.M.Ustinov Phys.Rev.B 68 075409 (2003)
The comparison between theory and experiment
for Ge on Si(100) “hut” islands
24
6.00E+010
Experiment
Theory
22
5.00E+010
Lateral size, nm
Surface density, cm
2
20
4.00E+010
3.00E+010
2.00E+010
18
16
Experiment
Theory
14
12
10
1.00E+010
410
8
420
430
440
450
460
470
0
Temperature, C
T
exp(  e ) 1
T )
N  ln(
T
T
480
490
500
510
410
420
430
440
450
460
470
480
490
500
510
520
530
0
Temperature, C
L  exp(ED / kbT )
MBE parameters of the system were: h=0.9nm, V=0.0345ML/s
A.A.Tonkikh et. al. Phys.Stat.Sol.(b) 236 No.1 R1 2003
Sb impact on the growth of Ge islands
Tsub=550°C, fast GR
with Sb
with Sb
Fast growth rate V=0.2A/s
10
12
6.0x10
Black - with Sb
Red - w/o Sb
10
-2
10
8
4.0x10
(1)
(2)
6
10
4
2.0x10
2
unexpected
0.0
0
550
560
570
580
590
Substrate temperature, °C
600
height,nm
Tsub=550°C, slow GR
w/o Sb
with Sb
w/o Sb
Density, cm
w/o Sb
Tsub=600°C, fast GR
Band-edges alignment of Si-Ge heterostructures
Band alignment for 1 Ge layer *
Band alignment for multilayer Si-Ge **
*N.V.Vostokov et.al. Phys.Sol.St. 2004 v.46(1) p.63
e-
CB
**O.G.Schmidt et.al. Phys.Rev.B. 2000 v.62(24) p.16715
CB
Ge
e-
Si
Si
hh+
E
z
Indirect optical transition
(in real space and k-space)
with aid of TO phonon
hh+
hh+
II-type of band-edge alignment
Ge e-
Ge
e-
e-
Si
VB
Ge
Ge
e-
Si
hh+
hh+
hh+
Si
Si
Si
II-type of band-edge alignment
Possibility to create a miniband
in the conduction/valence band.
? - parameters of the structure
Properties of highly strained Si/Ge superlattice
PL vs GR
T = 10 K
TEM plan view and cross-section
A : GR = 0.02 A/s
B : GR = 0.2 A/s
Low temperature
PL spectra
PL intensity [a. u.]
SI (0.90eV)
PL vs GR
T = 300 K
WL1
TO+O
TA
Si
LI1 (0.87eV)
A
WL2
BE
Si
LI2 (0.83eV)
0.8
PL Int. [a. u.]
G
Si
B
0.2 A/s
0.02 A/s
Si
TO
Si
0.9
1.0
1.1
Photon energy [eV]
TO
QDs
Room temperature
PL spectra
0.8
0.9
1.0
1.1
1.2
QDSL
1.3
Room temperature
EL spectra
EL intensity [a. u.]
Photon energy [eV]
2
TO
Si
There are still two open questions: 1) Absolute EL intensity?
2) Time resolved measurements?
0.7
0.8
0.9
2.8
j [A/cm ]: 2.6
2.4
1.0
1.1
Photon energy [eV]
2.2
2.0
1.8
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
1.2
Au impact on the properties of the multilayer structure
SIMS  Au~1016cm-3
19
4
197
79
Au
Huge mass
(atomic radius)
point defects and misfit dislocations
I-group element
(deep acceptor)
nonradiative recombination center
RT PL spectra
PL (a.u.)
Is it possible to avoid the misfit dislocations?
reference sample
Sample
with gold
800
1000
1200
1400
 (nm)
1600
1800
Conclusion
!
Good corellation between experimental and theoretical data was
demonstraited for the size and density distribution in ansamble
of Ge island on a Si(100) surface.
!
Unexpected Ge island array morphology was observed for
surfactant (Sb) mediated growth.
!
Strong room temperature electroluminescence from Si/Ge multilayer
structure was demonstrated.
Future tasks:
To give the explanation of unexpected Sb influence on
the Ge island array morphology.
The optimization of the multilayer structure MBE parameters
in order to get higher luminescence.
Time-resolved measurements.
Absolute EL intensity measurements with mesa-structure LED.
Cross-section scheme
Gold wire
Gold ring
Contact place
Cap Si n+
Si p+
(former substrate)
Active zone
(light emitting)
Al bottom
contact
Plan-view image of
the Si LED mesa-structure