1. Royal Holloway University of London
Towards passive terahertz imaging using a semiconductor quantum dot sensor
Vladimir Antonov
Royal Holloway University of London

2. 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

3. Passive Imaging with superconducting bolometer by VTT-NIST
Nb superconducting
bolometer
Detection of hidden weapon
Courtesy of VTT-NIST

4. 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

5. Some numbers for consideration
Plank’s law
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.
Passive imaging
U, J /(Hz m3)
f , THz
T=305K
U, J /(Hz m3)
T=300K
f , THz

6. Finger prints of explosives
Complex materials has a unique
fingerprints in spectrum
T=300K
JF Federici et all ’05

7. QD as a spectral sensitive detector
Layout of the QD in 2DEG
SEM images of the QD
Resonance curve
APL ’02 B
(Tesla) 1 2 3 4 5 20 40 60
Frequency  (/cm) c
 0
QD in magnetic
field
Zero filed
Plasma resonance in QD

8. Log-periodic circular antenna (0.2-3Thz)
QD-SET detector
Log-periodic circular antenna (0.2-3Thz)
coupled with QD sensor
Energy diagram
Dark switches and photo-response
original
peaks
shifted
DVg
SET response to QD excitation

9. Modeling of QD-SET SET SG1 CG Offset charge at SET SG2 QD QSET -Vc
NSET
NSET+1
-Vc

10. Formation of QD Individual SET trace 2D map of SET current
Charging of the QD

11. Photosignal at 0.3K
T=0.3K
T=0.05K

12. Photo response and dark counts
Noise Equivalent Power~ 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

13. Photosignal at K

14. 2D maps of QD-SET VS, V VS, V VC, V VC, V Emitter is OFF Emitter is ON
Physica E ’06
PRB’06

15. Detector of different designs
A lateral sensor with QD crossing
the channel
A lateral sensor with QD outside channel
A lateral sensor with QD
inside channel
A vertical sensor

16. QD outside of 2DEG channel
Gate
QD-SET

17. QD inside the 2DEG channel

18. QD in high magnetic field
LL0
LL1
SEM picture of the QD 1m
NATURE, 2000

19. QD in high B QD under illumination Time traces of QD conductance
Spectral sensitivity of the detector

20. QD in high B LL1­ I II QD has three levels: LL0­,LL0¯,
Lifetime of excitations
PRB, 2002

21. LT THZ microscope of Tokyo University
Ikushima, Komiyama APL, 2006

22. LT THZ microscope of Tokyo University

23. Future plans: Quantum Dot in DQW heterostructure
Schematic view
Inter-well excitation in
asymmetric DQW
~1 THz

24. Near-field antennae Simulation of near-field antennae
Simulation of E-field

25. Near-field antenna

26. Challenges Room Temperature Imaging
QD detector: which type?
Room Temperature Imaging
Source of THz radiation for in-situ calibration
Physics of isolated QD in DW heterostructures

27. Vertical sensor in DQW heterostructure
An et all, PRB’07