Towards passive terahertz Towards passive terahertz imaging using a imaging using a

semiconductor quantum dot semiconductor quantum dot sensorsensor

Vladimir AntonovRoyal Holloway

University of London

http://www.teraeye.com

AcknowledgmentsAcknowledgments

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 Passive Imaging with superconducting bolometer by superconducting bolometer by

VTT-NISTVTT-NIST

Nb superconducting bolometer Detection of hidden weapon

Courtesy of VTT-NISTCourtesy of VTT-NIST

Some numbers for considerationSome numbers for consideration

Background limited noise BLIP~ T(F/n)1/2 , where F - frame rate

(10Hz), n - number of detected photons (108), ~0.05K

Noise Equivalent Temperature Difference (NETD)

imposed by the temperature contrast, or variation of

spectral intensity (spectral fingertips) < 0.1K

Detector should have NETD better than 0.1K and

counting rate around 108 photons/sec

Some numbers for considerationSome numbers for consideration

Plank’s law

100 200 300 400 500

0.5

1

1.5

2T=305K

T=300K

f , THz

U,

10-1

9 J

/(H

z m

3 )

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

0.5 0.6 0.7 0.80.75

1.25

1.5

1.75

2

2.25

U,

10-2

1 J

/(H

z m

3 )

f , THz

Finger prints of explosivesFinger prints of explosives

Complex materials has a unique fingerprints in spectrum

T=300K

JF Federici et all ’05

QD as a spectral sensitive QD as a spectral sensitive detectordetector

Layout of the QD in 2DEG SEM images of the QD

222

0

2

cc

B (Tesla)0 1 2 3 4 5

0

20

40

60

Fre

quen

cy

(/c

m)

c

0

QD in magnetic field

Zero filed

Plasma resonance in QD

Rm

ne

1

4~

22

0

Resonance curve

APL ’02

QD-SET detectorQD-SET detector

eC1

2

0

EF

QDSET

Energy diagram

Dark switches and photo-response

radiation is ON

radiation is OFF

SE

T c

urr

ent,

arb

7525

Time,sec

Log-periodic circular antenna (0.2-3Thz) coupled with QD sensor

Conduct

ance

Gate voltage, Vg

original peaks

shifted peaks

Vg

SET response to QD excitation

Modeling of QD-SETModeling of QD-SET

CSD

CCD

CSS

CSS

C1S

R1S

C2S

R2S

C1D

R1D

C2D

R2D

ND

NS

VS VC

VSD

CC

CGSG1

SG2

SET

QD D

DCC

DSS

CSCC

SSSSET eNCVCV

C

CCVCVQ

Offset charge at SET

21 CCCCCC DC

DSC

QSE

T

NSET NSET+1

-Vc

Formation of QDFormation of QD

020

0-2.75 -2.70

VC (V)

I (p

A)

S

ICharging of the QD

-4.0 -3.8 -3.6 -3.4V

S,V

I S, a

rb. u

nits

2D map of SET current Individual SET trace

Photosignal at 0.3KPhotosignal at 0.3K

T=0.05K T=0.3K

Photo response and dark counts Photo response and dark counts

APL, JAP, PRB, IEEE ’04-07

Noise Equivalent Power~ 10-20 Watt/Hz1/2

NETD = NEP/(2~0.01K

Quantum Efficiency ~1%

Spectral bandwidth ~ 1%

Operation temperature is limited by SET (up to 4K)

Photosignal at 0.5-0.7KPhotosignal at 0.5-0.7K

5

10

15

20

25

30

35

-2.20 -2.15 -2.10 -2.05 -2.00

0

30

60

90

120

Co

un

ts,s

-1

VC,V

Life

time

,ms

T=0.7Kphotoresponse

dark

5

10

15

20

25

30

35

-2.20 -2.15 -2.10 -2.05 -2.00

0

30

60

90

120

Cou

nts,

s-1

VC,V

Lifetime,m

s

T=0.5K photoresponse

dark

2D maps of QD-SET 2D maps of QD-SET

Emitter is ON

VC, VV

S,

V

Physica E ’06PRB’06

Emitter is OFF

VC, V

VS,

V

Detector of different Detector of different designsdesigns

A vertical sensor

A lateral sensor with QD crossing the channel

A lateral sensor with QD inside channel

A lateral sensor with QD outside channel

QD outside of 2DEG QD outside of 2DEG channelchannel

Gate

QD-SET

QD inside the 2DEG QD inside the 2DEG channelchannel

QD in high magnetic fieldQD in high magnetic field

CC 112

C2

Metal gates

Vg

EF LL1

LL2

LL0

LL1

NATURE, 2000

QD in high magnetic field

1

SEM picture of the QD

QD in high QD in high BB

light off

light on

-689 -688 -6870.0

0.2

0.4

0.6

Con

duct

ance

(e2 /h

)

Gate voltage (mV)

B=3.67 TT=0.05 K

0 5 10Time (sec)

light off

light on

Con

duct

ance

(e /h

)2

0.0

0.2

0.4

QD under illumination Time traces of QD conductance

Spectral sensitivity of the detector

QD in high QD in high BB

B(Tesla)

3.5

II II II II II II II II II II II

I I I I I I I II

3.73.6

-660

-665

-670

Con

trol

gat

e vo

ltage

(m

Vol

t)

Con

dact

ance

(arb

.uni

ts)

0

1

QD has three levels: LL0LL0LL1

I IILifetime of excitations

3.4 3.6 3.8 4.0 4.210

-3

10-2

10-1

1

101

102

103

104

6

98

7 5

43

2 1

Life

time

(s)

B (T)

PRB, 2002

LT THZ microscope LT THZ microscope of Tokyo Universityof Tokyo University

Ikushima, Komiyama APL, 2006

LT THZ microscope LT THZ microscope of Tokyo Universityof Tokyo University

Future plans: Quantum Dot in Future plans: Quantum Dot in DQW heterostructure DQW heterostructure

~1 THz

Schematic view Inter-well excitation in asymmetric DQW

Near-field antennaeNear-field antennae

50

Simulation of near-field antennae

Simulation of E-field

Near-field antenna

Near-field antennaNear-field antenna

Challenges 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 DQWVertical sensor in DQWheterostructureheterostructure

An et all, PRB’07