Time-Correlated Single Photon
Counting (TCSPC)
Scott Thalman
Brigham Young University
Advisor: Dr. John Colton
Dr 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



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100 picosecond time resolution with deconvolution
InGaAs Quantum Dots
Optical properties are an indicator of sample quality
Photoluminescence
Excited States
(conduction band)
ee
Excitation
-
Relaxation
Photon
Energy Gap
Ground State
(valence band)
-
e
-
e
Quantum Dots
QD
GaAs
InGaAs
GaAs
40 nm
Scanning tunneling micrograph
of InGaAs Quantum Dots on
GaAs substrate
Dong Jun Kim et al 2008 Nanotechnology 19 47560
Quantum Dots
Confined electrons must occupy energy
states that fulfill the Schroedinger equation
Results:
•
•
Energy

Discrete energy levels
Discrete luminescence
wavelengths
http://www.vectorsite.net/tpqm_02.html
QD Photoluminescence
Sample 032607A, 3K, 780nm, .3s Tau, 8% Duty, Files 3-6, 2010-07-09
Power (Abitrary Units)
1E-9
405mW (3002.2W/cm^2)
270mW (2001.5W/cm^2)
180mW (1334.3W/cm^2)
120mW (889.5W/cm^2)
1E-10
1E-11
1E-12
1000
1200
Wavelength(nm)
1400
Time Correlated Single Photon Counting
Pulsed Laser
~30 fs, center wavelength 800 nm
14 Apr 2010 Haeyon Sample 032607-A
File 3
Counts
100000
10000
60
70
Laser: 1.6 mW (Focus 3.5in in front of sample)
25-30fs pulse 4.5 min
Card Thresh: Start Falling -0.3mV Stop Rising +0.34mV
AOM: 300 ns delay 200 ns width
Ref: 300 ns delay 30 ns width
80
90
100
110
Fast
Photodiode
Detector
120
Time (ns)
Lenses and Filters
Start
Ortec Fast Digitizer
Timing Module
Stop
Si-APD
Detector
QD
Sample
QD Fluorescence Lifetime
Expected Results
Fig 1
Fig 2
Fluorescence lifetime of InGaAs Quantum Dot (fig 1) and
Quantum Well (fig 2) samples measured by a streak camera.
Mazur et al 2006 Journal Of Applied Physics 100 054313
InGaAs QD Results
14 Apr 2010 Haeyon Sample 032607-A
File 3
Counts
100000
19 Apr 2010 All Samples Unfocused (normalized) Files 3-6
1
10000
70
80
90
100
110
120
Time (ns)
0.1
Counts
60
Laser: 1.6 mW (Focus 3.5in in front of sample)
25-30fs pulse 4.5 min
Card Thresh: Start Falling -0.3mV Stop Rising +0.34mV
AOM: 300 ns delay 200 ns width
Ref: 300 ns delay 30 ns width
032907:
t1= 1.77ns
t2= 3.7ns
0.01Response
Instrument
032607-A:
t1= 1.54ns
t2= 3.5ns
032607-B:
t1= 1.56ns
t2= 3.7ns
IRF:
t= 1.00ns
1E-3
70
75
Laser: 9 mW approximately 0.2W/cm^2
25-30fs pulse 2 min 3.7 K 510K counts
Card Thresh: Start Falling -0.3mV Stop Rising +0.34mV
AOM: 300 ns delay 200 ns width
Ref: 300 ns delay 30 ns width
80
85
Time (ns)
90
95
100
InGaAs QD Results:
Convolution
Definition of Convolution
Convolution Theorem

f (t )  g (t )  h(t ) 

FT ( f  g )  FT (h)  2 FT ( f ) FT ( g )
f (t ) g (t  t )dt

Example Of Deconvolution using Sample 032607-A
Apr 19 2010 Sample 032607-A (Focused)
File 9
File 9
Data: g9_B
Model: ExpDec1
Equation: y = A1*exp(-x/t1) + y0
Weighting:
y
No weighting
Deconvolution
IRF
Measured Data
0.6
Normalized Counts
Normalized Counts
0.9
0.3
0.6
Chi^2/DoF
= 0.00004
R^2
= 0.99916
y0
A1
t1
-0.00163
0.74229
0.64574
±0.00177
±0.00585
±0.0106
0.3
0.0
0.0
0
10
Time(ns)
-4
-2
0
2
Time(ns)
4
6
8
10
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
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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