Post on 27-Dec-2015
Strong scattering of light in Strong scattering of light in silicon nanowires formed by silicon nanowires formed by
metal-asmetal-asssisted chemical etchingisted chemical etching A. Efimova
Moscow State M.V. Lomonosov University, Physics Department
Nanomeeting2005, Minsk, 26—29 May, 2015
A. TkachevA. EliseevD. PresnovV. TimoshenkoT. NychyporukYu. Ryabchikov
Minsk, 26-29 May, 2015
Why MACE silicon nanowires?Why MACE silicon nanowires?
What for? APPLICATION
What’s different? What’s new?What’s novel? What’s peculiar?
PROPERTIESPROPERTIES LINEAR OPTICSLINEAR OPTICS
EXTREMELY LOW or EXTREMELY LOW or
HIGH REFLECTIONHIGH REFLECTION How comesHow comes??
Minsk, 26-29 May, 2015
Just a simple, reliable and cheap procedure
1. Ag nanoparticles deposition onto Si substrate in the aqueous solution of AgNO3
2. Ag nanoparticles-assisted chemical etching of Si substrates in the aqueous HF and H2O2 solution
3. Ag nanoparticles removal by rinsing in concentrated HNO3
Silicon nanowires (SiNWs)Silicon nanowires (SiNWs)First formed in the middle-1960s by vapour-liquid-solid (VLS) technique
Metal-assisted chemical etching - MACEMetal-assisted chemical etching - MACE
Minsk, 26-29 May, 2015
V. Sivakov, F. Voigt, B. Hoffmann, et al. Wet - Chemically Etched Silicon Nanowire Architectures: Formation and Properties // Nanowires - Fundamental Research – 2011, p. 45-80. V. Sivakov, S. Christiansen. Novel discovery of silicon // J. Nanoelectron. Optoelectron. 2012. V.7. N6. P. 583-590.
КК..ВВ. . БуньковБуньков, , ЛЛ..АА. . ГолованьГоловань, , КК..АА. . ГончарГончар и др.и др.. . Зависимость эффективности комбинационного рассеяния света в Зависимость эффективности комбинационного рассеяния света в ансамблях кремниевых нанонитей от длины волны возбуждения // Физика и техника полупроводников – 2013. ансамблях кремниевых нанонитей от длины волны возбуждения // Физика и техника полупроводников – 2013. Т.47. В.3, С. 329-333.Т.47. В.3, С. 329-333.
Columnar PrismaticBunched PyramidalTilted ZigzagCotton-like Flaky
Structure: Si(100)Structure: Si(100) andand SiSi(111)(111)
What are MACE SiNWs?What are MACE SiNWs?
Minsk, 26-29 May, 2015
... ... What’s peculiar?What’s peculiar?
- Variety of individual SiNW shapes Variety of individual SiNW shapes
- Variety of SiNW lateral dimensions Variety of SiNW lateral dimensions
BUTBUT
-- Dense arrays of SiNWs with comparableDense arrays of SiNWs with comparable
lateral dimension and interwire spacelateral dimension and interwire space
- Free of catalyst contamination - Free of catalyst contamination
Minsk, 26-29 May, 2015
PROPERTIES: Low reflection Low reflection at normal incidence at normal incidence Black silicon Black siliconSTRUCTURE: Pyramidal shape, thin layers Pyramidal shape, thin layers
J.-Y. Jung, Zh. Guo, S.-W. Jee, et al. A strong antireflective solar cell prepared by tapering silicon nanowires // Optics Express – 2010. V.18. N103, p.A286-A292, p.A286-A292
Bunched
Tapered
c-Sic-SiBlack silicon
Minsk, 26-29 May, 2015
PROPERTIES: High reflection High reflection in Near-InfraredSTRUCTURE: Columnar shape, thick layersColumnar shape, thick layers
A=1–T–R
6000 8000 10000 120000
20
40
60
80
100
Abso
rption (%
)Wavenumber (cm-1)
6000 8000 10000 120000
20
40
60
47%
54%
Tota
l Refl
ecta
nce
(%
)
Wavenumber (cm-1)
c-Si L = 1.3 m L = 8.0 m L = 23 m
56%E
g
2 1,8 1,6 1,4 1,2 1 0,8 Wavelength (m)
15-20% 15-20% increase in Rincrease in REntirely diffuseEntirely diffuse
6000 8000 10000 120000
20
40
60E
g
Tota
l Tra
nsm
itta
nce
(%
)
Wavenumber (cm-1)
2 1,8 1,6 1,4 1,2 1 0,8 Wavelength (m)
c-Si substratec-Si substrate
Minsk, 26-29 May, 2015
STRUCTURE: STRUCTURE: What’s peculiar?What’s peculiar?
Lateral dimensionsLateral dimensions
Columnar wires 1 m SEM
Interwire space 1 m SEM
Inner channels 100 nm TEM, SEM
Surface nanostructures 5–10 nm TEM
8
11 mm 11 mm
What are SiNWs under study?What are SiNWs under study?
Minsk, 26-29 May, 2015
Radiative transport equation&Diffusion Radiative transport equation&Diffusion approximation: Applicability approximation: Applicability
-- Radiative transport ls generated a media a media
- Light diffusion is generated before absorption - Light diffusion is generated before absorption
- Light diffusion is generated in a restricted layer - Light diffusion is generated in a restricted layer
- Scatterers are pointwise and independent - Scatterers are pointwise and independent 2
,
(3 10)
(2 )
s a
a tr
tr
s
l l
l l
L l
l a
0
0 0
(1.25 0.8)
2eff
m
n
PROPERTIES: How comes?How comes?
2
02 2( ) BB p
a
DD I z z
t z L
1
3
3
( )
Е trB
a tr a
tr s a
lD
L l
l
v
Minsk, 26-29 May, 2015
Diffusion approximation: Diffusion approximation: Diffuse reflectance. StaticsDiffuse reflectance. Statics
Types of variablesTypes of variables
1) 1) Table:Table: substratesubstrate
2) 2) Directly measured:Directly measured: LL,, RRdd
3) Obtained from the interference fringers in the effective medium spectral range: nneffeff
44) ) Calculated:Calculated: zz1,21,2((nneffeff, , substratesubstrate), ),
55) ) Estimated or got from photoacoustics: aa
Infinite media (solid line) Infinite media (solid line) and a layer of the thickness and a layer of the thickness L L in the air in the air ((dash linedash line)), , L L == 55lltrtr
O. L. Muskens, J.G. Rivas, R.E. Algra, O. L. Muskens, J.G. Rivas, R.E. Algra, et alet al. Design of Light Scattering in Nanowire Materials for Photovoltaic Applications // . Design of Light Scattering in Nanowire Materials for Photovoltaic Applications // Nano Letters – 2008, V.8, N.9, p. 2638-2642.Nano Letters – 2008, V.8, N.9, p. 2638-2642.
2
1 2 1 22
sinh cosh
1 sinh cosh
tr tr
a a a
a a aa
L l z L l
L L Ld z z L z z L
L L LL
R
PROPERTIES: How comes?How comes?
1
1 2
3
( )
, extrapolation lengths
a tr a
tr s a
L l
l
z z
Transport mean free path to be extractedTransport mean free path to be extracted
Minsk, 26-29 May, 2015
Transport mean free path of light.Transport mean free path of light. Static resultsStatic results
Transport mean free path valueTransport mean free path valuemeets the demands of diffusion approximationmeets the demands of diffusion approximation
0,
m
1.250 0.800
1000 cm 12 m
L, m 8 24 8 24
ltr m
1 1a
4.0±0.4 6.0±0.6 2.5±0.3 3±0.3
Minsk, 26-29 May, 2015
Diffusion approximation: Diffusion approximation: Time-resolved reflection. DynamicsTime-resolved reflection. Dynamics
2
21 2
1
d a
D D
L z zL
1
1 2
2 2 211 2
21 2
1 cos23
( ) exp( )
exp( )
tr
ntr a
l zn
L z zD DtR t
l L z z L n Dt
L z z
-500 0 500 1000
-0,1
0,0
0,1
0,2
0,3
0,4
-1000 -500 0 500 1000 1500
1E-5
1E-4
1E-3
0,01
0,1
I cr (re
l.un.
)
Time (fs)
I (a
rb. units)
Time delay (fs)
2
2
1( ) lim ( ) *( τ)
T
cr in scatT
T
I E t E t dtT
Cross-correlation functionCross-correlation function
Cr4+:forsterit laser ultrashort pulses (60 fs), repetition rate 80MHz
At long timesAt long times
Minsk, 26-29 May, 2015
Transport mean free path of light:Transport mean free path of light: Static and dynamic resultsStatic and dynamic results
L = 24 m, = 1,250
m
Statics
Dynamics
6.0±0.6
5.0±0.5
Minsk, 26-29 May, 2015
ConclusionConclusion
The reflection of thick silicon nanowire layers in The reflection of thick silicon nanowire layers in
the near-infrared range below and above the the near-infrared range below and above the
band gap is well understood by assuming the band gap is well understood by assuming the
diffusion-like radiative transport in silicon diffusion-like radiative transport in silicon
nanowire array.nanowire array.
Minsk, 26-29 May, 2015
Stone Forest of ShilinStone Forest of Shilin
Thank you for your attentionThank you for your attention