Download - Jean-Christophe DELAGNES [email protected]
Ultrafast carrier dynamicsUltrafast carrier dynamicsin Br+-bombarded semiconductorsinvestigated by
Optical Pump - THz ProbeOptical Pump - THz Probespectroscopy
Jean-Christophe [email protected]
April 2009 JPU 2009 2
Outline
• IntroductionIntroduction• Experimental SetupExperimental Setup• Samples preparationSamples preparation• ResultsResults
– InPInP– InGaAsInGaAs
• PespectivesPespectives
April 2009 JPU 2009 3
Introduction & Motivations
• Generation of coherent terahertz pulses in ultrafast semiconductors (LT-AsGa and other materials)
• Specific methods aim to increase the concentration of traps:– Film growth and Doping– Implantation or Irradiation with heavy ions
• Ionic irradiation: efficient method of engineering the carrier lifetime. How are the carrier lifetime How are the carrier lifetime and dynamics affected?and dynamics affected?
• Present study: Transient Terahertz Spectroscopic Transient Terahertz Spectroscopic study of the effect of Brstudy of the effect of Br++ irradiation irradiation of InGaAs of InGaAs and InP on the carrier lifetime and mobilityand InP on the carrier lifetime and mobility
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 4
Why using THz in SC science?
• THz Radiation is indeed a valuable tool for (true) optoelectronics studies
ElectronicsGunn Diodep-i-n DiodeHigh mobility transistor (HEMT)
OpticsNL OpticsUltrafast LasersQCL
April 2009 JPU 2009 5
Why using THz in SC science?
• THz Radiation is indeed a valuable tool for (true) optoelectronics studies
ElectronicsGunn Diodep-i-n DiodeHigh mobility transistor (HEMT)
OpticsNL OpticsUltrafast LasersQCL
April 2009 JPU 2009 6
Experimental SetupPump:=810 nm (fs, CPA)
Probe:Broadband (ps) THz
Collinear Pump-Probe
Geometry: Ultimate Temporal Resolution (limited only by thedetector
response)<ps
Low excitation experiment: few µJ/pulse – w0~2mmInitial carrier concentrations: 1016<n0<1018 cm-3
Setup in vacuum box to prevent water absorption
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 7
Experimental SetupPump:=810 nm (fs, CPA)
Probe:Broadband (ps) THz
Collinear Pump-Probe
Geometry: Ultimate Temporal Resolution (limited only by thedetector
response)<ps
Low excitation experiment: few µJ/pulse – w0~2mmInitial carrier concentrations: 1016<n0<1018 cm-3
Setup in vacuum box to prevent water absorption
IntroductionSetupSamples ResultsPespectives
Optical Rectification(‘0’ frequency DFG)
(2)(,;~0)
ETHz(t)Iopt(t)
April 2009 JPU 2009 8
Experimental SetupPump:=810 nm (fs, CPA)
Probe:Broadband (ps) THz
Collinear Pump-Probe
Geometry: Ultimate Temporal Resolution (limited only by thedetector
response)<ps
Low excitation experiment: few µJ/pulse – w0~2mmInitial carrier concentrations: 1016<n0<1018 cm-3
Setup in vacuum box to prevent water absorption
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 9
Experimental SetupPump:=810 nm (fs, CPA)
Probe:Broadband (ps) THz
Collinear Pump-Probe
Geometry: Ultimate Temporal Resolution (limited only by thedetector
response)<ps
Low excitation experiment: few µJ/pulse – w0~2mmInitial carrier concentrations: 1016<n0<1018 cm-3
Setup in vacuum box to prevent water absorption
IntroductionSetupSamples ResultsPespectives
ETHz(t): Transient modifications of ETHz(t) (waveform) are recorded in time for different pump-probe delays
Equilibrium Photoexcitation RelaxationScattering
April 2009 JPU 2009 10
Experimental SetupPump:=810 nm (fs, CPA)
Probe:Broadband (ps) THz
Collinear Pump-Probe
Geometry: Ultimate Temporal Resolution (limited only by thedetector
response)<ps
Low excitation experiment: few µJ/pulse – w0~2mmInitial carrier concentrations: 1016<n0<1018 cm-3
Setup in vacuum box to prevent water absorption
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 11
Samples Preparation
0
1
2
3
4
5
6
7
8
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
In0.47Ga0.53As InP
0 3 6 0
1
2
3
4
5
6
7
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
InP
0 3 6
Depth (µm) 0 3 6
InP
0.0
0.2
0.4
0.6
0.8 D
ensi
ty o
f int
rinsi
c ra
diat
ion
indu
ced
defe
cts
(108 c
m–3
/cm
–2) 0.9
0.7
0.5
0.3
0.1
Depth (µm) 0 3 6
In0.47Ga0.53As InP
0.0
0.2
0.4
0.6
0.8
1.0
Den
sity
of i
ntrin
sic
radi
atio
n in
duce
d de
fect
s (1
08 cm
–3/c
m–2
)
11 Mev Br+ ions: deep implantation
IntroductionSetupSamples ResultsPespectives
[Br] [Br]
[def] [def]
April 2009 JPU 2009 12
Samples Preparation
0
1
2
3
4
5
6
7
8
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
In0.47Ga0.53As InP
0 3 6 0
1
2
3
4
5
6
7
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
InP
0 3 6
Depth (µm) 0 3 6
InP
0.0
0.2
0.4
0.6
0.8 D
ensi
ty o
f int
rinsi
c ra
diat
ion
indu
ced
defe
cts
(108 c
m–3
/cm
–2) 0.9
0.7
0.5
0.3
0.1
Depth (µm) 0 3 6
In0.47Ga0.53As InP
0.0
0.2
0.4
0.6
0.8
1.0
Den
sity
of i
ntrin
sic
radi
atio
n in
duce
d de
fect
s (1
08 cm
–3/c
m–2
)
11 Mev Br+ ions: deep implantation
Bulk InPBulk InP
IntroductionSetupSamples ResultsPespectives
[Br] [Br]
[def] [def]
Stopping Range of Ions in the Matter
April 2009 JPU 2009 13
Samples Preparation
0
1
2
3
4
5
6
7
8
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
In0.47Ga0.53As InP
0 3 6 0
1
2
3
4
5
6
7
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
InP
0 3 6
Depth (µm) 0 3 6
InP
0.0
0.2
0.4
0.6
0.8 D
ensi
ty o
f int
rinsi
c ra
diat
ion
indu
ced
defe
cts
(108 c
m–3
/cm
–2) 0.9
0.7
0.5
0.3
0.1
Depth (µm) 0 3 6
In0.47Ga0.53As InP
0.0
0.2
0.4
0.6
0.8
1.0
Den
sity
of i
ntrin
sic
radi
atio
n in
duce
d de
fect
s (1
08 cm
–3/c
m–2
)
11 Mev Br+ ions: deep implantation
Etched InPEtched InP
IntroductionSetupSamples ResultsPespectives
[Br] [Br]
[def] [def]
April 2009 JPU 2009 14
Samples Preparation
0
1
2
3
4
5
6
7
8
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
In0.47Ga0.53As InP
0 3 6 0
1
2
3
4
5
6
7
Impl
anta
tion
dens
ity (1
03 cm
–3/c
m–2
)
Depth (µm)
InP
0 3 6
Depth (µm) 0 3 6
InP
0.0
0.2
0.4
0.6
0.8 D
ensi
ty o
f int
rinsi
c ra
diat
ion
indu
ced
defe
cts
(108 c
m–3
/cm
–2) 0.9
0.7
0.5
0.3
0.1
Depth (µm) 0 3 6
In0.47Ga0.53As InP
0.0
0.2
0.4
0.6
0.8
1.0
Den
sity
of i
ntrin
sic
radi
atio
n in
duce
d de
fect
s (1
08 cm
–3/c
m–2
)
11 Mev Br+ ions: deep implantation
InGaAsInGaAs
IntroductionSetupSamples ResultsPespectives
[Br] [Br]
[def] [def]
April 2009 JPU 2009 15
InP: Results
• Slow SamplesTransient modifications of the peak in the THz waveform vs. Pump-Probe delay p (1D Scan).Spectrally averaged (unresolved) information about the carrier lifetime c
Time Resolved detection of the Terahertz waveform: Complex spectrum (Real & Imag. part) of the surface conductivity
InPInP
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 16
InP: Results• Slow Samples
Surface conductivity
InPInP
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 17
InP: Results• Fast Samples
FT along time FT along pump-probe delay
Time dependent spectrum
2D spectrum
Dynamics in 1011 and 1012 cm-2 samples is very fast (no quasi-dc analysis) 2D Fourier transformation provides a proper deconvolution
H. Němec, et al., J. Chem. Phys. 122, 104503 (2005)
TimeDependentWaveforms
InPInP
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 18
InP: Results• Fast Samples
20 0
p 1 1 1eff p
1 1( , )2 2s c c
n ef fm if if
InPInP
Experimental 2D spectrum of the surface conductivity
Drude model Fit
Residuum exhibits no features
GOOD AGREEMENT WITH A DRUDE MODEL
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 19
InP: Results• Power Dependence
tht
t
h
hhh
h
hett
t
h
h
t
t
e
et
tet
t
e
eee
e
ngNnn
zn
Dtn
ggnNnn
Nnn
tn
ngNnn
zn
Dtn
2
2
2
2
1
1
Shockley-Read modelShockley-Read model
1
1 exp
1 exp
ee t
e t B
ghh t
h t B
N EgN k T
E ENgN k T
0 10 20 30Pump-probe delay (ps)
5
4
3
2
1
0
103 S
(-1
)
Sample E10n0 = 0.9×1017 cm-3
n0 = 2.2×1017 cm-3
n0 = 4.9×1017 cm-3
Large pump spot:No transverse diffusionNo transverse diffusion
InPInP
IntroductionSetupSamples ResultsPespectives
Phys. Rev. B, 78, 235206 (2008)
April 2009 JPU 2009 20
InP Results: Summary Sample nIRRAD (cm–3) nBr (cm–3) n0 (cm–3) s (fs) 0 (cm2V–1s–1) decay (ps)
B9 2×1016 0 1.6×1017 140 3000 490
E9 9×1016 5×1012 1.1×1017 120 2600 70
B10 2×1017 0 1.6×1017 120 2700 100
E10 9×1017 5×1013 0.9×1017 100 2100 5.5
B11 2×1018 0 1.6×1017 70 1600 2.6
E11 9×1018 5×1014 2.2×1017 90 2100 1.2
B12 2×1019 0 1.6×1017 40 900 0.29
Influence of Br+ ion concentration on Bulk and Etched sample parameters
Carriers lifetime:-Due to density of induced defects-Not significantly influenced by Br implantation
Trapping time decreases Trapping time decreases by 3 orders of by 3 orders of magnitude (Log)magnitude (Log)
Mobility decreases only Mobility decreases only by a factor 3 (Linear)by a factor 3 (Linear)
InPInP
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 21
InGaAs: Results• Slow Samples
Dose(cm–2)
s
(fs)c
(ps) R/R(ps)
0,THz 0,Hall
(cm2V–1s-1)
109 0.25 297 ± 5 >500(*) 2600 10800
1010 0.22 43± 5 10 2100 --
1011 0.175 3.4± 2 <0.4 1900 4300
0 10 20 30 40 50time ps
3
2
1
0
Det
ecte
d si
gnal
(a.u
.)
C scan Sample B 5mWC scan sample A 5mWC scan Sample C 5mw
InGaAsInGaAs
(*)undoped
IntroductionSetupSamples ResultsPespectives
Single Component
April 2009 JPU 2009 22
In1-xGaxAs: Results
• Fast Samples
InGaAsInGaAs
(x=0.47)
-4 -3 -2 -1 0 1 2 3 4f p (THz)
-2-1.5
-1-0.5
00.5
11.5
2
f (TH
z)
0
3000
6000
9000
theo(fp,f)1,2,3
ii
Conductivity: Sum of several contributions (3 paths)
IntroductionSetupSamples ResultsPespectives
Excitation
Ground state
State 2 (L-valley)State 1 (-valley)
c,1
23
c,2
Drude response (s,2)State 3 (-valley)
c,3
13
12
21
Fit of the 2D spectrumgives access to the ’s
April 2009 JPU 2009 23
In1-xGaxAs DynamicsInGaAsInGaAs
(x=0.47)
mL = 0.29 me
mX = 0.68 me
IntroductionSetupSamples ResultsPespectives
m = 0.041 me
April 2009 JPU 2009 24
In1-xGaxAs DynamicsInGaAsInGaAs
(x=0.47)
mL = 0.29 me
mX = 0.68 me
IntroductionSetupSamples ResultsPespectives
m = 0.041 me
April 2009 JPU 2009 25
In1-xGaxAs DynamicsInGaAsInGaAs
(x=0.47)
mL = 0.29 me
mX = 0.68 me
IntroductionSetupSamples ResultsPespectives
m = 0.041 me
April 2009 JPU 2009 26
In1-xGaxAs DynamicsInGaAsInGaAs
(x=0.47)
mL = 0.29 me
mX = 0.68 me
IntroductionSetupSamples ResultsPespectives
m = 0.041 me
… and further slow relaxation …
April 2009 JPU 2009 27
In1-xGaxAs DynamicsInGaAsInGaAs
(x=0.47)
mL = 0.29 me
mX = 0.68 me
IntroductionSetupSamples ResultsPespectives
m = 0.041 me
… Somehow complicated …
Improvement of the theoretical model byS.E.Ralph et al, Phys. Rev. B 54, 5568
April 2009 JPU 2009 28
ConclusionTime-resolved THz spectroscopy in Br+-bombarded : InP & In0.53Ga0.47AsCharacterization of : Lifetime & Mobility
For density of induced defects (not [Br+]) both Lifetime and Mobility
InP (Most irradiated):• carrier lifetime 3 orders of magnitude• mobility of carriers only reduced by factor 3only reduced by factor 3 (vs. as-grown sample)• carrier trappingtrapping and carrier diffusiondiffusion
In1-xGaxAs: • As found in InP, both electron mobility and lifetime are reduced• Very high photoexcited mobilityVery high photoexcited mobility 3600 cm2V–1s–1 + 460 fs lifetime • Changing x and [Br+] : large tunabilty of optical and electronic material
parameters Improvement of ultrafast optoelectronic devices based on this material. High potentialHigh potential for THz optoelectronicTHz optoelectronic at 1.5 µm1.5 µm
April 2009 JPU 2009 29
Perspectives
• Wavelength dependence:– Penetration depth / Initial profile– Electronic State
• Temperature dependence • Clusters of defects• Automated Measurement:
– Single shot waveform + pump-probe– Single shot 2D
IntroductionSetupSamples ResultsPespectives
April 2009 JPU 2009 30
Subpicosecond Non Contact Ohmmeter
April 2009 JPU 2009 31
Acknowledgments
• CPMOH
• Sample preparation, dc and optical characterisation
• Experiment hosted in Prag
• Support for international exchange
E.N’Guema, L.Canioni, P.Mounaix
H.Němec, L.Fekete, F.Kadlec, P.Kužel
M.Martin, J.Mangeney
Thank you for Thank you for your attentionyour attention