X-ray Characterization of Si-doped InAs nanowires on GaAs(111) substrate
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Transcript of X-ray Characterization of Si-doped InAs nanowires on GaAs(111) substrate
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X-ray Characterization of Si-doped InAs nanowires on GaAs(111) substrate
Saqib Muhammad Prof. Dr Ullrich Pietsch
DESY 19.03.2013
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Outline Introduction a. Applications and growth of nanowires (NWs)b. Structure of NWs
Aim or Motivationa. Doping Influenceb. The effect of Oxide layer on NWs growth
Resultsa. Sample Imagesb. Exprimental technique (XRD)c. Expriment and Resultsd. Conclusion e. Out look
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IntroductionWhy semiconductor nanowires?-For studying new phenomena at nanometric one dimensional length.
-Used as building blocks for electronic and optoelectronic devices.
Why structural study?
-The electrical and optical properties of the material changes with the change in the structural parameters.-Therefore the structure of the nanowirs is more important.
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Zincblend(ZB):Stacking ABCABC
Wurtzite(Wz)Stacking ABABAB
accwz awz
ZB and WZ have slightly different lattice parameters!
Crystal Structure InAs(narrow band gap, high e mobility, small effective mass)
cwz > 2/sqrt(3) ac
awz < 1/sqrt(2) ac
1. Structural composition varies among NWs
2. Strain accommodation at interfaces?
GaAs
InAs
ac=5.653Å
ac=6.085Å
Δa/a
=7.1
%
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1) To determine the efects of etched and non-etched Oxide-layer on NW‘s growth mechanisam?
Etched Oxide-layerGaAs (111)B substrates, covered with a thin layer of Hydrogen Silsesquioxan (HSQ SiOx);the HSQ is etched in very diluted HF to ~ 6 nm thickness.
Aim of the WorkIn this talk, we present a X-ray diffraction study of the influences of Si-doping in InAs NWs grown on GaAs(111) substrate using In-assisted MBE growth.
UnetchedGaAs (111)B substrates, covered with a thin layer of Hydrogen Silsesquioxan (HSQ SiOx), unetched;
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Samples
1μm1μm
a) Undoped b) Si doped 1x1017 cm-3 c) Si doped 5x1017 cm-3
d) Si doped 1x1018 cm-3 e) Si doped 5x1018 cm-3
1.2μ
m
100nm
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Experimental technique
d
Asymmetrical Symmetrical
n λ = 2dhkl sinαf ↔ |q| = 2π/d
qx = 2π/λ (cos(2Ѳ-αi) – cos(αi)
qz= 2π/λ (sin(αi) + sin(2Ѳ-αi)
X-ray experiments have been performed at ESRF synchrotron-source in Grenoble. XRD was employed at Id01 beam line using a x-ray wavelength of λ=1.239 Å and a 2D PILATUS DETECTOR.
ωQy
Qx
q
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Undoped Si- 5x10 17cm-3 Si- 1x10 18cm-3
GaAs(111)
Δa/a
=7.1
%
01234567891011121314
Inte
nsity
Symmetric (111) reflection
InAsNW
(a) (b) (c)Series one
Qz=19.25nm-1
Qz=17.98nm-1
Qz=18.20nm-1
∆Qz=0.21nm-1
NWd1
d2
d1
a=5.984Åa=6.058Å
∆a=1.2%
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Series one
Lattice constant6.058Å5.653Å4.130Å5.430Å
InAsGaAs AsSi
d2
Using Vegard‘s law
In0.77 Ga0.23 As
a = xaInAS (1-x)aGaAs As
d2 Alloy formation
The alloy formation explain by surface diffusion of Ga librated through small holes created during etching process
Comparison between symmetric(111) and asymmetric reflection(331) of undoped and Si-doped 1x1018 cm-3
Undoped(111)
(331)
(331)
(111)
ZB(NW)Qz=41.85Qx=-17.40
ZB(Alloy)Qz=42.40Qx=-17.61
Doped
Zb(331)a=6.044 Å(-17.31, 41.82)
Zb(111)a=6.047 Å
qx nm-1
cw /aw =1.658
WZ(105)
q z nm
-1
Wz(105)a=4.221 ÅC=7.001 Å(44.51, -17.48)
∆a=1.2%
a=5.984Å
J. Bauer et al., 2009ApPhA..96..851B
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Series two
Undoped Si- 1x10 17cm-3 Si- 5x10 19cm-3
Symmetric (111) reflection Undoped and Si-doped InAs NWs , cover with a thin layer (HSQ→SiOx), unetched.
GaAS
InAS
No Alloy formation
Parasitic islands
NW(331)
Asymmetric (331) reflection
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ConclusionIn Conclusion, the hetroepitexial growth behavior of InAs NWs on GaAs was investegated
Combination of etching and Si-doping produce an alloy with seprate lattice parameter in Series one
The alloy has zinc-blend structure
After analyzing of above 5 samples by X-ray diffraction we found that the 2nd or unknown peak can‘t be attribute to Si. Its attribute to an alloying of Substrate (Ga) and wire material (InAs)
NW‘s have zinc-blend structure with small contribution wurtzite
In case of non-etcehed samples the alloy peak is not observed, for highly doped sample InAS peaks keep the same shape like for undoped sample
No measurable influence of doping on structure
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Acknowledgements
Prof. Dr. Ullrich Pietsch University of Siegen
Dr. Andreas Biermanns University of Siegen
Anton Davydok University of Siegen
Dr. Mikhail Lepsa Jülich Forschungszentrum
Dr. Thomas Grap Jülich Forschungszentrum
Thank you for your attention!
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Focussed Beam Expriment
λ= 1.23 Å Beam size=300x300nm2 Focal length=129mm
Nanofocus set-up
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Low temprature processing Precise control dopping growth rate precisely control (0.01 to 0.3 μm/min) Ultra high vacuum 10-8 to 10-10 torr
Sample preperation (MBE)
Varian GEN-II-MBE
Liquid Au droplet is replaced by a drop formed group IIIA meterial itself. In, Ga etc.Controlled supply of As and In in UHV at elevated substrate temperatures NWs growth rate → 0.3-0.4 μm/h Substrate Temprature → 530°C
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Series two
Undoped Si- 1x10 17cm-3 Si- 5x10 19cm-3
Symetric (111) reflection
01234567891011121314
Undoped and Si-doped InAs NWs , cover with a thin layer (HSQ→SiOx), unetched.
GaAS
InAS
No Alloy formation
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lattice constants Peak 1 Peak 2Peak 3
d1 = 6.085Åd2
d3 = 5.967Å
different materials involved in the growth process, simplest case:Substrate (GaAs) and adsorbate (InAs) with identical crystal structure
Series one
d3
Using Vegard‘s law
In0.77 Ga0.23 As
a = xaInAS (1-x)aGaAs As
d3 Alloy formationThe alloy formatin explainby surface diffusion of GaLibrated through small holesCreated during etching process
Lattice constant
6.058Å5.653Å4.130Å5.430Å
InAsGaAs AsSi
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Zincblend(ZB):Stacking ABCABC
Wurtzite(Wz)Stacking ABABAB
accwz awz
ZB and WZ have slightly different lattice parameters!
Crystal Structure InAs(narrow band gap, high e mobility, small effective mass)
cwz > 2/sqrt(3) ac
awz < 1/sqrt(2) ac
1. Structural composition varies among NWs
2. Strain accommodation at interfaces?
Si
GaAs
ac= 5.430Å
ac=5.653Å
Δa/a
=11%