Ultrafast carrier dynamicsUltrafast carrier dynamicsin Br+-bombarded semiconductorsinvestigated by

Optical Pump - THz ProbeOptical Pump - THz Probespectroscopy

Jean-Christophe DELAGNESjc.delagnes@cpmoh.u-bordeaux1.fr

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 Setup

Pump:=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 Setup

Pump:=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 Setup

Pump:=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 Setup

Pump:=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 Setup

Pump:=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

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–2)

Depth (µm)

In0.47Ga0.53As InP

0 3 6 0

1

2

3

4

5

6

7

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–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 in

trin

sic

radi

atio

n in

duce

d de

fect

s (1

08 cm

–3/c

m–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

intr

insi

c ra

diat

ion

indu

ced

defe

cts

(108 c

m–3

/cm

–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

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–2)

Depth (µm)

In0.47Ga0.53As InP

0 3 6 0

1

2

3

4

5

6

7

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–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 in

trin

sic

radi

atio

n in

duce

d de

fect

s (1

08 cm

–3/c

m–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

intr

insi

c ra

diat

ion

indu

ced

defe

cts

(108 c

m–3

/cm

–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

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–2)

Depth (µm)

In0.47Ga0.53As InP

0 3 6 0

1

2

3

4

5

6

7

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–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 in

trin

sic

radi

atio

n in

duce

d de

fect

s (1

08 cm

–3/c

m–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

intr

insi

c ra

diat

ion

indu

ced

defe

cts

(108 c

m–3

/cm

–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

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–2)

Depth (µm)

In0.47Ga0.53As InP

0 3 6 0

1

2

3

4

5

6

7

Im

plan

tati

on d

ensi

ty (

103 c

m–3

/cm

–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 in

trin

sic

radi

atio

n in

duce

d de

fect

s (1

08 cm

–3/c

m–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

intr

insi

c ra

diat

ion

indu

ced

defe

cts

(108 c

m–3

/cm

–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 SamplesSurface 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 f

m 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

ngN

nn

z

nD

t

n

ggnN

nn

N

nn

t

n

ngN

nn

z

nD

t

n

2

2

2

2

1

1

Shockley-Read modelShockley-Read model

1

1exp

1exp

ee t

e t B

ghh t

h t B

N Eg

N k T

E ENg

N k T

0 10 20 30Pump-probe delay (ps)

5

4

3

2

1

0

10

3

S (

-1)

Sample E10

n0 = 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 5mW

C scan sample A 5mW

C 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 4

f p (THz)

-2-1.5

-1-0.5

00.5

11.5

2

f (T

Hz)

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 spectrum

gives 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

Conclusion

Time-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