Time-Correlated Single Photon Counting (TCSPC)

Scott Thalman Brigham Young University

Advisor: Dr. John ColtonDr Haeyeon Yang USU Physics

Help from Mitch Jones, Steve Brown, Dallas Smith

Overview Time-correlated single photon counting

(TCSPC) measures photoluminescence (PL) lifetimes Pulsed laser illumination source Single-photon detectors Very fast timing module

100 picosecond time resolution with deconvolution

InGaAs Quantum Dots Optical properties are an indicator of

sample quality

Photoluminescence

e-

e-

e-

Excitation Relaxation

Ground State(valence band)

Excited States(conduction band)

PhotonEnergy Gap

e-

GaAs

Quantum Dots

Scanning tunneling micrograph of InGaAs

Quantum Dots on GaAs substrate

Dong Jun Kim et al 2008 Nanotechnology 19 47560

GaAs

QD

40 nm

InGaAs

Quantum Dots Confined electrons must occupy

energy states that fulfill the Schroedinger equation

Results:• Discrete energy

levels• Discrete

luminescence wavelengths

http://www.vectorsite.net/tpqm_02.html

Ene

rgy

QD Photoluminescence

1000 1200 1400

1E-12

1E-11

1E-10

1E-9

P

ower

(Abi

trary

Uni

ts)

Wavelength(nm)

120mW (889.5W/cm^2)180mW (1334.3W/cm^2)270mW (2001.5W/cm^2)

405mW (3002.2W/cm^2)

Sample 032607A, 3K, 780nm, .3s Tau, 8% Duty, Files 3-6, 2010-07-09

Time Correlated Single Photon Counting

QDSample

Pulsed Laser~30 fs, center wavelength 800 nm

Si-APDDetector

Fast Photodiod

e Detector

Ortec Fast DigitizerTiming Module

Start

Stop

60 70 80 90 100 110 120

10000

100000

Laser: 1.6 mW (Focus 3.5in in front of sample)25-30fs pulse 4.5 minCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width

File 314 Apr 2010 Haeyon Sample 032607-A

Cou

nts

Time (ns)

Lenses and Filters

QD Fluorescence Lifetime Expected

Results

Mazur et al 2006 Journal Of Applied Physics 100 054313

Fluorescence lifetime of InGaAs Quantum Dot (fig 1) and Quantum Well (fig 2) samples measured by a streak camera.

Fig 2Fig 1

70 75 80 85 90 95 1001E-3

0.01

0.1

1

Laser: 9 mW approximately 0.2W/cm^225-30fs pulse 2 min 3.7 K 510K countsCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width

19 Apr 2010 All Samples Unfocused (normalized) Files 3-6

Cou

nts

Time (ns)

032607-B:t1= 1.56nst2= 3.7ns

032607-A:t1= 1.54nst2= 3.5ns

032907:t1= 1.77nst2= 3.7ns

IRF: t= 1.00ns

InGaAs QD Results

60 70 80 90 100 110 120

10000

100000

Laser: 1.6 mW (Focus 3.5in in front of sample)25-30fs pulse 4.5 minCard Thresh: Start Falling -0.3mV Stop Rising +0.34mVAOM: 300 ns delay 200 ns widthRef: 300 ns delay 30 ns width

File 314 Apr 2010 Haeyon Sample 032607-A

Cou

nts

Time (ns)

Instrument Response

InGaAs QD Results:Convolution

( ) ( ) ( ) ( ) ( )f t g t h t f t g t t dt

Definition of Convolution

( ) ( ) 2 ( ) ( )FT f g FT h FT f FT g

Convolution Theorem

-4 -2 0 2 4 6 8 10

0.0

0.3

0.6

Apr 19 2010 Sample 032607-A (Focused) File 9

Data: g9_BModel: ExpDec1Equation: y = A1*exp(-x/t1) + y0Weighting: y No weighting Chi^2/DoF = 0.00004R^2 = 0.99916 y0 -0.00163 ±0.00177A1 0.74229 ±0.00585t1 0.64574 ±0.0106

Nor

mal

ized

Cou

nts

Time(ns)0 10

0.0

0.3

0.6

0.9

Nor

mal

ized

Cou

nts

Time(ns)

DeconvolutionIRFMeasured Data

Example Of Deconvolution using Sample 032607-A File 9

Summary of Results

Sample Number

Photoluminescent Lifetime (ns)

Unfocused Laser

Focused Laser

032607-A 0.86 0.65

032607-B 0.78 0.78

032907 0.96 0.60

Conclusion Using TCSPC we were able to measure

the photoluminescent lifetimes of self-assembled InGas QDs to help determine their quality.

Our samples had lifetimes of 0.6-1.0 ns. Using deconvolution we were able to

enhance our results. Future studies will determine if

quantum structures such as QD chains can be formed by this growth method.Thank

You