Towards passive terahertz
imaging using a semiconductor
quantum dot sensor
Vladimir Antonov
Royal Holloway
University of London
http://www.teraeye.com
Acknowledgments
Royal Holloway, UK : H Hashiba
Tokyo University&JST, Japan: Prof. S Komiyama, Drs. J
Chen, O Astafiev (NEC)
ISSP RAN, Russia: Dr. L Kulik
NPL, UK: Dr A Tzalenchuk, Dr S Gibling and P Kleinschmidt
Chalmers University, Sweden: Prof. P Delsing, Dr S Kubatkin
Optisense LTD: M Andreo
Passive Imaging with superconducting
bolometer by VTT-NIST
Nb superconducting
bolometer
Detection of hidden weapon
Courtesy of VTT-NIST
Some numbers for consideration
Noise Equivalent Temperature Difference (NETD) imposed
by the temperature contrast, or variation of spectral
intensity (spectral fingertips) < 0.1K
Background limited noise BLIP~ T(F/n)1/2 , where F - frame rate
(10Hz), n - number of detected photons (108), ~0.05K
Detector should have NETD better than 0.1K and counting
rate around 108 photons/sec
Some numbers for consideration
Passive imaging
2
U, 10-21 J /(Hz m3)
U, 10-19 J /(Hz m3)
Plank’s law
T=305K
1.5
1
T=300K
0.5
100
200
f , THz
300
400
500
2.25
2
1.75
1.5
1.25
0.75
0.5
0.6
0.7
0.8
f , THz
There is a difference in ~1010 photons/sec
(~10-23J) for black body radiation at 300K
and 305K in bandwidth from 0.5 to 0.7
THz.
Finger prints of explosives
Complex materials has a unique
fingerprints in spectrum
T=300K
JF Federici et all ’05
QD as a spectral sensitive detector
Layout of the QD in 2DEG
SEM images of the QD
Resonance curve
Frequency  (/cm)
Plasma resonance in QD
QD in magnetic
field
60
2
4neZero
 filed
0 ~
m  1R
2 40
0
20
0
APL ’02

0
1

c
c
 c 
2





0
2
 2 
2

2
B
(Tesla)
3
4
5
QD-SET detector
Energy diagram
SET
QD
0
EF
e2
C1
Dark switches and photo-response
SET response to QD excitation
radiation is OFF
Conductance
DVg
SET current, arb
Log-periodic circular antenna (0.2-3Thz)
coupled with QD sensor
original
peaks
shifted
radiation
is ON
peaks
Vg
25 Gate voltage, 75
Time,sec
Modeling of QD-SET
SET
SG1
CG
Offset charge at SET
QD
SG2

VSD
C   CC  C SD  CCD  C1  C 2
S
S
C1 R1
N
S
S
S
C
VS
CC
C
N
D
D
S
C2 R2
NSET
S
S
C
D
S
C1 R1

CC
VS C SD  VC CCD  eN D
C
VC
D
C
C
NSET+1
QSET
S

QSET  VS C SS  VC CCS 
D
D
C2 R2
D
-Vc

Formation of QD
Individual SET trace
IS, arb. units
-4.0
-3.8
-3.6
VS,V
I S (pA)
200
Charging of the QD
I
0
2D map of SET current
-2.75 -2.70
VC (V)
-3.4
Photosignal at 0.3K
T=0.05K
T=0.3K
Photo response and dark counts
Noise Equivalent Power~
10-20 Watt/Hz1/2
NETD = NEP/(2hkBDnt1/2
~0.01K
Quantum Efficiency ~1%
Spectral bandwidth ~ 1%
Operation temperature is
limited by SET (up to 4K)
APL, JAP, PRB, IEEE ’04-07
Photosignal at 0.5-0.7K
120
T=0.5K
35
photoresponse
120
60
20
15
30
dark
-1
Counts,s
Counts,s
25
photoresponse
90
25
60
20
15
30
dark
10
0
30
10
0
-2.20 -2.15 -2.10 -2.05 -2.00
VC,V
5
-2.20 -2.15 -2.10 -2.05 -2.00
VC,V
5
Lifetime,ms
90
Lifetime,ms
-1
30
35
T=0.7K
2D maps of QD-SET
Emitter is OFF
VS, V
VS, V
Emitter is ON
VC, V
VC, V
Physica E ’06
PRB’06
Detector of different designs
A lateral sensor with QD crossing
the channel
A lateral sensor with QD
inside channel
A lateral sensor with QD outside channel
A vertical sensor
QD outside of 2DEG channel
QD-SET
Gate
QD inside the 2DEG channel
QD in high magnetic field
QD in high magnetic field
SEM picture
of the QD
C1
Metal
gates
EF
C12
C2
Vg
1m
LL2
LL1
LL1
LL0
NATURE, 2000
QD in high B
QD under illumination
0.4
Conductance (e /h)
Conductance (e2/h)
0.6
Time traces of QD conductance
2
B=3.67 T
T=0.05 K
light off
light on
0.2
0.0
-689
-688
Gate voltage (mV)
-687
Spectral sensitivity of the
detector
0.4
light on
0.2
light off
0.0
0
5
Time (sec)
10
QD in high B
QD has three levels:
Lifetime of excitations
LL0,LL0,
LL1
II
I
4
10
3
2
7 5
1
6
10
10
9
1
10
-1
10
-2
10
-3
3.4
4
1
3
8
3.6
PRB, 2002
3.8
B (T)
4.0
4.2
I
-660
I
I
I
II II II
I I
I
I
II II II
II II II
I
II II
1
-665
0
-670
3.5
3.6
B(Tesla)
3.7
Condactance (arb.units)
2
Control gate voltage (mVolt)
Lifetime (s)
10
LT THZ microscope
of Tokyo University
Ikushima, Komiyama APL, 2006
LT THZ microscope
of Tokyo University
Future plans: Quantum Dot in DQW
heterostructure
Schematic view
Inter-well excitation in
asymmetric DQW
~1 THz
Near-field antennae
Near-field antenna
Simulation of near-field antennae
50m
Simulation of E-field
Near-field antenna
Challenges
 QD detector: which type?
 Room Temperature Imaging
 Source of THz radiation for in-situ calibration
• Physics of isolated QD in DW heterostructures
Vertical sensor in DQW
heterostructure
An et all, PRB’07