Aspects of Si-Ge heteroepitaxial system

Coffee seminar 03 of December 2003

Tonkikh Alexander

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

Max-Planck Institute of Microstructure Physics

Ioffe Physical-Technical Institute

Dr.hab. George E. CirlinDr.hab. Vladimir G.DubrovskiiDr.Vyacheslav A.EgorovProf.Dr.hab. Viktor M.Ustinov

Outlook

Ioffe Institute presentation

Brief introduction into Si-Ge MBE technique

Ge islands on a Si (100) surface

Si-Ge multilayer structure

Kinetics of the islands formationAbnormal Sb impact

Band structureMultilayer structure propertiesAu impact

Conclusion

Ioffe Physical-Technical Institute194021 Politechnicheskaya 26, Saint-Petersburg, Russiahttp://www.ioffe.rssi.ru

Founded in 1918 by Abram Fedorovich Ioffe.Ioffe-effecthole conductivity conception

Scientific adviser:Nobel-prize winnerZhores I. Alferov*

*Double heterostructure laser inventor

The main old building during winter time.

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

Center of Nanoheterostructure Physics Division of Solid State ElectronicsDivision of Solid State PhysicsDivision of Plasma Physics, Atomic Physics and Astrophysics Division of Physics of Dielectric and Semiconductors Educational Center

Physics of SemiconductorHeterostructures Laboratory

Head: Zh.I. Alferov

Deputy Head:Victor M. Ustinov

Deputy Head:Nikolai N. LedentsovResearch activities:

* 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

http://www.ioffe.rssi.ru/sem_tech/

Institute departments

Silicon MBE

Principle of operation Real setup Riber Siva-45

Si substrateTsub

Si source Ge source

TSi TGe

MBE conditions:HV/UHV P<10-6torrTsub<Tsi and Tge

in situ control

P~10-9torrin situ control: RHEED, QMS

Si-Ge heteroepitaxial system

Si bulk (substrate)

Ge bulk

Si substrate

Ge epilayer

aSi=5.431Å

Both diamond (face-centered cubic) like structure

aGe=5.658Å

Δ= 2(aGe- aSi)/(aGe + aSi)x100%=4%

dGe < 4ML

x

y

axGe=aSi

ayGe>aGe

Metastable epitaxial layer against islanding and misfit dislocation formation

Island formation

Stranski-Krastanow growth mode

Ge islands on a Ge wetting layer

In situ observation of the island formation

Reflection High Energy Electron Diffraction system (RHEED)

Ee~30KeV, λe = h/(2meEee) ~ 0.1Å

substrateE-gun screen

Flat 2x1 reconstruction of Si(100) surface

Surface with Ge islandsStart (p=0)

Finish (p=198)

P1 (p=40)P0 (p=60-80)P2 (p=110)

The dynamic of RHEED pattern intensity on a white section

0 20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80

90

P2P0P1

Spo

t Int

ensi

ty, %

Position, pixel

d=0ML d=3.4A d=4.2A d=6.3A d=6.5A d=6.6A d=6.8A d=7A

dGe=0Å

dGe=7Å

2D-3D transition at 6.8Å (=4.8ML)of Ge!

~ 1-4°

Ex situ observation of the Ge on Si islands

Atomic force microscopy (tapping mode)

Bimodal island shape distribution

huts <105> domeshuts+domes

Phase diagramfor Ge islandson Si (100) surface

440 460 480 500 520 540 560 580 600

1.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5

10.010.511.0

Huts

Domes

Isla

nds

heig

ht, n

m

Substrate temperature, 0C

5.5Å Ge

8.5Å Ge

AFM RHEED

RHEEDAFM

N=3.1x108cm-2

N=3.3x1010cm-2

Tsub=500°C Tsub=550°C Tsub=600°C

Kinetics of Ge islands formation*

* V.G.Dubrovskii, G.E.Cirlin and V.M.Ustinov Phys.Rev.B 68 075409 (2003)

Ge WL

Si

Ge island

h

Free energy of coherent island formation:

L

ihlhk

h

hF

LF

ihlzF

FFFiF

attr

surf

attrsurfelas

elas

020

000

0

2)cos(

)(

020

20

)exp(

0)0(

0)(1

)(

2/3

2

0

ln4

Q

Q

T

Th

lN

e

eq

Equation of material balance:

t

eq tgdlhhtVdthh0 0

2

32

00

//

0 ),()(

i=2/3

V(t) - growth rate

The parameters of the system after the relaxation stage:

2/13/1

0

0

2

0 lncot

)(

2

3

Q

Qan

T

T

h

hHdlL e

eq

eq

R -new variable

g(,t) - island size distributiong(,0)=0,

2/1

ln5

21

QT

Thh e

eqc VT

TDQ

)(

The main growth mechanism is the diffusion of theatoms from the wetting layer to the islands with D(T).

410 420 430 440 450 460 470 480 490 500 510

1.00E+010

2.00E+010

3.00E+010

4.00E+010

5.00E+010

6.00E+010 Experiment Theory

Sur

face

den

sity

, cm

2

Temperature, 0C

The comparison between theory and experiment

410 420 430 440 450 460 470 480 490 500 510 520 530

8

10

12

14

16

18

20

22

24

Experiment Theory

Late

ral s

ize,

nm

Temperature, 0C

for Ge on Si(100) “hut” islands

A.A.Tonkikh et. al. Phys.Stat.Sol.(b) 236 No.1 R1 2003

TTTT

N

e

1)

)exp(ln(

)/exp( TkEL bD

MBE parameters of the system were: h=0.9nm, V=0.0345ML/s

Sb impact on the growth of Ge islands

Tsub=600°C, fast GR

Tsub=550°C, slow GR

w/o Sb with Sb

Tsub=550°C, fast GR

w/o Sb with Sb

w/o Sb with Sb

550 560 570 580 590 600

0.0

2.0x1010

4.0x1010

6.0x1010

unexpected

Den

sity

, cm

-2

Substrate temperature, °C

0

2

4

6

8

10

12Black - with SbRed - w/o Sb

(1) (2)

Fast growth rate V=0.2A/s

he

igh

t,nm

Band-edges alignment of Si-Ge heterostructures

Band alignment for 1 Ge layer *

Ge

II-type of band-edge alignment

hh+

Si Si

e-CB

VB

*N.V.Vostokov et.al. Phys.Sol.St. 2004 v.46(1) p.63

Indirect optical transition (in real space and k-space)with aid of TO phonon

Band alignment for multilayer Si-Ge **

**O.G.Schmidt et.al. Phys.Rev.B. 2000 v.62(24) p.16715

hh+

CB

II-type of band-edge alignment

Si Si

Ge

Si

Ge

Si

Ge

Si

Ge

e-

e- e-

e-e-

hh+hh+ hh+

hh+

Possibility to create a minibandin the conduction/valence band.

? - parameters of the structure

E

z

Properties of highly strained Si/Ge superlattice

0.7 0.8 0.9 1.0 1.1 1.2

2.82.62.42.22.01.81.61.51.41.31.21.11.00.90.80.70.60.5

j [A/cm2]:

SiTO

QDSL

EL

inte

nsity

[a. u

.]Photon energy [eV]

0.8 0.9 1.0 1.1

A : GR = 0.02 A/sB : GR = 0.2 A/s

PL vs GRT = 10 K

A

B

WL2

LI2 (0.83eV)

WL1

SI (0.90eV)

LI1 (0.87eV)

SiTO+OG

SiBE

SiTA

SiTO

PL

inte

nsity

[a. u

.]

Photon energy [eV]

Low temperature PL spectra

0.8 0.9 1.0 1.1 1.2 1.3

PL vs GRT = 300 K

0.2 A/s 0.02 A/s

QDs

SiTO

PL

Int.

[a. u

.]Photon energy [eV]

Room temperature PL spectra

Room temperature EL spectra

There are still two open questions: 1) Absolute EL intensity? 2) Time resolved measurements?

TEM plan view and cross-section

Au impact on the properties of the multilayer structure

197

79

19

4 Au

SIMS Au~1016cm-3

Huge mass (atomic radius)

I-group element(deep acceptor)

point defects and misfit dislocations nonradiative recombination center

800 1000 1200 1400 1600 1800

Sample with gold

RT PL spectra reference sample

PL

(a.u

.)

(nm)

Is it possible to avoid the misfit dislocations?

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.

!

Strong room temperature electroluminescence from Si/Ge multilayerstructure 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 parametersin order to get higher luminescence.

Time-resolved measurements.

Absolute EL intensity measurements with mesa-structure LED.

! Unexpected Ge island array morphology was observed for surfactant (Sb) mediated growth.

Plan-view image of the Si LED mesa-structure

Si p+

(former substrate)

Active zone(light emitting)

Cap Si n+

Gold ring

Al bottom contact

Contact place

Gold wire

Cross-section scheme