Optoelectronic and Nonlinear Optical Processes
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Optoelectronic and Nonlinear Optical Processes. in Low Dimensiona Organic and Inorganic Semiconductors. Bhanu P. Singh Department Of Physics Indian Institute of Technology Bombay, Mumbai- 400076.

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Optoelectronic and Nonlinear Optical Processes

in Low Dimensiona Organic and Inorganic Semiconductors

Bhanu P. Singh

Department Of Physics

Indian Institute of Technology Bombay, Mumbai- 400076


Nonliear optical systems, Nonlinearity & Its influence on opto - electronic response in low-d quantum confined systems

Information Stress on Technology


Patterns in nature opto - electronic response in low-d quantum confined systems


Spatial pattern in a fluid heated from below opto - electronic response in low-d quantum confined systems


Kerr slice with feedback mirror opto - electronic response in low-d quantum confined systems

Theoretical model


Pattern generation in saturable absorber opto - electronic response in low-d quantum confined systems

Thresholdintensity is given by

where  is given by following equation


Artificial design of complexity opto - electronic response in low-d quantum confined systems

Nonlinear optical system to simulate 2-component reaction-diffusion system dynamics

System with 2 Kerr slices and bounded feedback loops

Variety of patterns


Some observed patterns opto - electronic response in low-d quantum confined systems

Application to information processing


Isolated States as memories opto - electronic response in low-d quantum confined systems


Quest for photonic materials opto - electronic response in low-d quantum confined systems

Capacity for tailoring the optical properties such as

(3)  Eg-n and   r -3

Property relationship with structure, interactions and ensuing processes

Conjugated Polymers

 Semiconductors


Microscopic origin of nonlinearity opto - electronic response in low-d quantum confined systems


B.P.Singh et al,JCP109,685(1998) opto - electronic response in low-d quantum confined systems


B.P.Singh et al,Europhys.lett.45,456(1999) opto - electronic response in low-d quantum confined systems


PPV : optoelectronic material opto - electronic response in low-d quantum confined systems

B.P.Singh et al,JNOPM,7,571(1998)


Quantum confined 0 d semiconductors

- opto - electronic response in low-d quantum confined systems

LUMO

R

surface states

PL emission

+

non-radiative

transition

primary

absorption

HOMO

Surface states in semiconductor nanoparticles

Quantum confined 0-d semiconductors

Quantum dot transition probability  spatial restriction

Surface states provide highly efficient nonradiative channels and significantly quench the photoluminescence yield


Nanocomposites of CdS and ZnO opto - electronic response in low-d quantum confined systems

EDAX and TEM - Approximately stoichiometric CdS and ZnO

(Cd:S = 1:1.20 and Zn:O = 1:1.18)


SHUTTER opto - electronic response in low-d quantum confined systems

PRESSURE

GAUGE

GAS FLOW

LN2-COOLED

SUBSTRATE

HOLDER

MAGNETRON

GUN

TURBO

PUMP

VIEW

PORT

SCRAPER

RF magnetron sputtering - Experimental setup


Tunable source opto - electronic response in low-d quantum confined systems

Detector

Sample

Linear absorption spectroscopy

Itr= Iine-at


l opto - electronic response in low-d quantum confined systemsexc

Monochromator + PMT

Comparative study of PL in CdS and CdS:ZnO nanocomposite films

sample

Vasa, Singh and Ayyub (in preparation)


Decay-time measurement opto - electronic response in low-d quantum confined systems

Faster decay  higher PL yield


l opto - electronic response in low-d quantum confined systemsemi

lexc

film

lexc = 458 nm

Coherent PL from nanocomposite

thin films

Multiple beam interference observed in PL spectra

Vasa, Singh and Ayyub (submitted) J. Phys. Cond. Mat


Ti:Sapphire opto - electronic response in low-d quantum confined systems

Laser System

100 MHz, 800 nm, 80 fs

BBO

Lock-in

Amplifier

400 nm

Slit separation = 178 mm

Slit width = 30 mm

Sample-slit = 6.15 cm

Slit-detector = 88.6 cm

PMT slit width ~ 1 mm

121 Hz

GG475

PMT

Sample

Double slit

Double slit experiment - Setup


Experimental results opto - electronic response in low-d quantum confined systems

Vasa, Singh and Ayyub J. Phys. Cond. Mat17,189(2005)


Photocurrent spectroscopy

Lockin opto - electronic response in low-d quantum confined systems

Tunablesource

sample

Powersupply

Photocurrent spectroscopy

Vasa, Singh, Taneja, Ayyub et. al, J. Phys. Cond. Mat, 14, 281 (2002)


Ir photocurrent spectroscopy
IR Photocurrent spectroscopy opto - electronic response in low-d quantum confined systems

Measurement against dark background  Higher sensitivity

Vasa, Singh and Ayyub (in preparation)


Pockels cell opto - electronic response in low-d quantum confined systems

Ti:Sapphire

Laser System

774 nm, 68 fs, 100 MHz

774 nm

68 fs, 3 Hz

l/2

polarizer

Data acquisition

PD2

PD1

50%

ARR

Variable

attenuator

HR

mirror

sample

R = 0.04

50%

R = 0.04

ARINS - Experimental setup


ARINS - Experimental setup opto - electronic response in low-d quantum confined systems


CdS thin film (thickness = 1.3 opto - electronic response in low-d quantum confined systemsmm)

  • Wavelength = 776 nm

  • Pulse width = 82 fs

  • Pulse rep. Rate = 3 Hz

  • Isample (max) ~ 0.8 GW/cm2

    b = 48 cm/ GW

b (CdS Single crystal) = 6.4 cm/GW at 780 nm


Dispersion of opto - electronic response in low-d quantum confined systemsb for a CdS:ZnO nano-composite thin film

b776nm

(cm/GW)

sample

CdS

(Single X´tl)

6.4

nano CdS

48

CdS:ZnO-2

129

  • Presence of mid bandgap states

  • Free carrier absorption

  • Significant one photon, photo-current observed in IR

Vasa, Singh and Ayyub (in preparation)


Quantitative measurement of opto - electronic response in low-d quantum confined systems

One photon resonant nonlinearity

Vasa, Singh and Ayyub (in preparation)


Ar opto - electronic response in low-d quantum confined systems+

oscilloscope

Ti:Sapphire

+ BBO

391nm 100MHz

detector

chopper

sample

Carrier dynamics by

pump-probe spectroscopy - Setup


Pump-probe spectroscopy - Results opto - electronic response in low-d quantum confined systems

Carrier generation and relaxation time measurement


LUMO opto - electronic response in low-d quantum confined systems

LUMO

non

radiative

transition

non

radiative

transition

PL emission

PL emission

secondary

absorption of

PL or probe

primary

absorption

of pump

primary

absorption

of pump

HOMO

HOMO

Origin of photo-darkening

Free carrier absorption

Excited state absorption

Photo-induced chemical and/or structural changes


Solutions of rate equations opto - electronic response in low-d quantum confined systems

LUMO

N4

N3

fast non-radiative

transition (~ps)

secondary

absorption of

pump/PL/ probe

(~ps)

non-radiative

transition

(~10ps, gb)

pl. emission

(~100ps, ga)

N2

primary

absorption

of pump

(~ps, b)

slow non-radiative

transition (~2ms, gc)

HOMO

N1

Proposed 4-level model

Vasa, Singh and Ayyub (in preparation)


Carrier generation and relaxation - opto - electronic response in low-d quantum confined systems

data fitting


PL as a function of intensity - z scan opto - electronic response in low-d quantum confined systems


PL spectra as a function of opto - electronic response in low-d quantum confined systems

incident intensity


  • Conclusions : opto - electronic response in low-d quantum confined systems

  • Self-organizing nonlinear optical system and information processing – enormous potential

  • Organic & inorganic low-d semiconductors – adaptable to property engineering

  • Constructive interference of one- and two-photon tributaries – must for large nonlinearity in organics by molecular engineering

  • Nonlinearity originating from exciton-phonon coupling – potential for NLO devices

  • Geometric ease in tailoring inorganic semiconductor quantum dots but organics have an edge

  • NLO processes may be detrimental to optoelectronic properties


Thank You opto - electronic response in low-d quantum confined systems

Acknowledgement

  • TIFR

  • Parinda Vasa

  • Prof. P. Ayyub

IITB

  • Prof. T. Kundu

  • A.V.V. Nampoothiri

  • Subal Sahani

  • Biswajit Pradhan

  • Binay Bhushan

  • Rajeev Sinha

Department of Science and Technology


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