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Oct 4 2006/ Seminar
Department of Physics / NTHU
On-Chip Optical-coupled Quantum Hall
Devices in THz range
Jeng-Chung Chen
Outline
The study of Single-electron transistor
•
Device characterization
•
Excited electronic states in
closed QD
•
Discussion
•
Conclusion
On-chip optical-coupled QH devices
•
Passive THz scanning
microscopes
•
Emitter: Hot spots
•
Detector QH detector
•
Device design
•
Future perspective
Introduction: Technological and biological length scales
Single Electron Transistor - Introduction
Lateral Confinement Technique
SEM picture
100nm
Capacitive Charging Model
Shadow Evaporation Technique
Eg.
diameter ~ 0.5-0.2m
Cg ~100-10 aF
C ~2-0.9 fF
Al
Device Characterization
Temperature: 70-100mK
(a)
Lithographic size of QD :
570nm560nm
Meta-stable states of QD observed by Al-SET
QD : source/dra in grounded
V SET SD  800V ( DC )  20V ( AC )
Qualitative Discussion
F0
V1=-1.18V
Discussion: Emperical Model
V1=-1.18V fixed
In closed QD, regime 2-6
U 2  e 2, 2 V 2   2,QD
U 1  e1, 2 V 2  1,QD
U QD
e2
N QD
C
e2
N QD
C
e2
 e QD, 2 V 2 
N QD
C
 2, 2   QD, 2  1, 2
Quantitative discussion
U 2  e( 2, 2   2,QD QD, 2 )V 2   2,QD
U 1  e(1, 2  1,QD QD, 2 )V 2  1,QD
U QD
e
U QD
e
 2   2, 2   2,QD QD, 2  0.33,  2,QD  0.885
1  1, 2  1,QD QD, 2  0.0122, 1,QD  0.233
N SET
1
Csg
2
Cc
(
)V 2  2 U QD
e
e
Cc~58.8aF, C1sg2=3.12aF
U1
U2
UQD
Conclusion – First part
1. Kinetics of charging and discharging of closed
quantum dots (QD) in a GaAs/AlGaAs heterostructure
crystal are studied by an Aluminum single electron
transistor (Al-SET) electrostatically coupled to the
quantum dot.
2. The period and conductance of CB peaks of Al-SET
associated with different gating conditions reveal
several distinct regimes, strongly depending on the
tunneling barriers of QD.
3. A lift-up and an uncovered sinking electron excited
state with long life time are realized in the completely
closed dot.
4. An empirical model is proposed to explain the
physical origins of these transitions.
Ref: J.C. Chen, et al. Phys. Rev. B, 74, 045321 (2006).
electronics
microwaves
MF, HF, VHF, UHF, SHF, EHF
100
103
106
kilo
mega
•
optics
THz
visible
x-ray
g -ray
0.3–30THz
109
1012
1015
1018
giga
tera
peta
exa
1021
zetta
1024 Hz
yotta
1 THz ~ 1 ps ~ 300 µm ~ 33 cm-1 ~ 4.1 meV
Molecular vibration/rotation, Energy levels of quantum structures, magnetic resonance,
collective excitations, transit times in mesoscopic devices, superconductor gaps…
Biology, chemistry, medics, physics, astronomy, homeland security,
environmental monitoring, non-destructive industrial testing,
agriculture, …
Detection of chemical drugs
Non-destructive
check of IC
Many applications
extensively discussed & studied
Mapping of
pharmaceutical tablets
Airport control
Security
Medical diagnostics
Science (2002)
Picometrix
Skin cancer
TeraView
THz Imaging and Sensing
Conventional approach
External
light source
Identification/characterization
Object
of the objects
THz detection
THz, NIR,
Visible
Scattered,
Reflected
Transmitted
P = nW-W
Example:
Daniel M. Mittleman et. al. IEEE Journal of Selected Topics in Quantum Electronics,
2, 679 (1996).
THz Imaging and Sensing
Our approach : Passive / noninvasive
Object
• Specific dynamics
of the object ?
THz Detection
emitted
P = 0.01fW-pW
Example:
• Activity in
natural state ?
Hall-bar emitter
XY stage
Hall bar
sample
Lens
holder
CuBe
spring
Si-SIL
Ref: K. Ikushima et al., Phys. Rev. Lett. 93,
146804(2004)
Temp: 4.2K, =2,
I=100A, CE: 100pW
Emitter: Hot spots in IQHE
+ ΔSD/
GaAs / AlGaAs heterostructure
S
2
ΔU(r)
D
-ΔSD/2
ħc = 10 meV
μS
N=3
-
-
-
-
-
-
-
S
●
D
B
+
μS
U(r)
+ + + + + +
Classical equi-potential lines in QH
states
Ref: Y.Kawano et al., Phys. Rev. B, 59, p.12537(1999)
μD
N=2
μD
N=1
U(r)
Δ μSD > ħωc /2
• Higher LLs are fed with
electrons via tunneling.
Detectors
f =13 THz,
Detectors
ε = 10 meV,
Sensitivity (NEP)
10-15 W/Hz1/2
(Cyclotron resonance, GaAs/AlGaAs 2DEG)
Quantum Hall (QH)
λ = 100μm, k = 100 cm-1
Speed
1ms
Narrowband
Tunability
k= 2 cm-1
Y.Kawano et al., JAP, 89, 4037 (2001)
H. Sakuma et al., Far-infrared Phys. & Technol., (2006)
400μm
C
400
μm
Lattice heating :
Te  TL  Te
TL =4.2K, Te ~2K
 R
Rxx   xx
 T

 Te

On-chip otical coupled quantum Hall devices
Ohmic contacts
Device design
GaAs/AlGaAs heterostructure
2DEG: n~1-2 1011cm1
 ~1-0.5 106 cm2V 1s 1
Temp: ~4.2K
B_field: ~6-7T
Optical consideration
2DEG
Light propagation
Absorption issue
Study subjects
Reference:
Ref. C. Wood et al. Appl. Phys. Lett. 88,142103(2006)
4mm
Organic polymer: benzocyclobutene (BCB)
1. Application: On-chip THz wave
propagation
(wave-guide design / switching rate)
2. Physics:
(1) Onset of CE in IQHE
(2) Temperature dependence
(3) FQHE ??
Biological activities
Bio-molecules
Bio-cell
H.Fujitani et al.,J. Chem. Phys. (2005)
• Cell thermometry
• Molecular “fingerprint” emission activated by ATP hydrolysis
Electron dynamics in semiconductors & metals
• Landau levels
• Size quantization
(QD, 2D-subband)
• Impurity levels
• Superconductor
• etc.
 -gaps
Future studies
Limitation: low temperature !
Objects
e.g. QPC in high magnetic field
Molecular
CNT….etc.
Wave guide / antenna design
THz photon
detector
Narrow band /Tunability
e.g.
Hall bar detector
QD / Al-SET detector
SIS detectors or mixers
CNT….etc.
Intensity of CE
Lowest: QD
Detected:
Highest: QHm
Pdetect = 0.01aW  0.1pW
Detector
Emission only from the focal point (10%)
10-4
Efficiency of optical system (5%)
Quantum efficiency of detector (5%)
Total emitted: Ptotal CE = 100 aW 100 pW
10-7
Energy conversion efficiency: 10-7
Electrical: P = RI
2=
3 nW 5 mW
-
e
-
+
QH device
I = 500nA  400 μA
I