1 viraj jayaweera department of physics astronomy
TRANSCRIPT
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Viraj Jayaweera
Department of Physics Astronomy
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GSU
Outline
Introduction
Dye-Sensitized Near-Infrared Detectors (DSID) 1/f Noise in DSID
Split-off Band Near-Infrared Detectors Interfacial Workfunction Internal Photoemission
(IWIP) Far-Infrared Detectors
Future Studies
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The Electromagnetic Spectrum
http://www.nasa.gov/centers/langley/science
Visible Micro wave near-IRnear-IR mid-IRmid-IR Far-IRFar-IR
0.8 – 5 m 5 - 30 m 30 - 300 m
Wavelength
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IR Wavelength Range Classification
–1-3 μm Short Wavelength Infrared SWIR
–3-5 μm Medium Wavelength Infrared MWIR
–5-14 μm Long Wavelength Infrared LWIR
–14-30 μm Very Long Wavelength Infrared VLWIR
–30-100 μm Far Infrared FIR
–100-1000 μm Submillimeter SubMM
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Applications
Infrared image of Orion
Human Suspect climbing over fence at 2:49 AM in total darkness
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Applications
Breast Cancer Blood Flow
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Applications
Electrical Hotspots
Energy Conservation
Bad Insulation spotsLoose
contacts
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Different Types of Infrared Detectors
Photon DetectorsPhoton Detectors
PhotovoltaicPhotovoltaicPhoto Conductive
Photo Conductive
Thermal DetectorsThermal Detectors
BolometerBolometer ThermopileThermopile
Pyroelectric Detectors
Pyroelectric Detectors
IR DetectorsIR Detectors
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GSU Dye-Sensitized Near-Infrared Detectors(DSID)
http://shs.starkville.k12.ms.us/~kb1/Hort1wk4.htm
n-TiO2 nanoparticle
Dye
p-CuSCN
V
n-type Dye p-type
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Dye-sensitized electron injection to a semiconductor
Light induced charge carrier generation in a semiconductor
Direct and Sensitized Photo-Injection
VB
CB
VB
CB
Semiconductor Dye
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Structure of Dye-Sensitized IR Detector
Dye
Platinum or Gold layer
p-CuSCN
n-TiO2
Transparent CTO
Glass
Glass TiO2 nanoparticles
CTO
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Energy Level Diagram
Appl. Phys. Lett., Vol. 85, No. 23, (2004)
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IR Absorbing Dyes
Anionic Dyes(readily anchor to the
TiO2 surface)
Cationic Dyes(Not directly ancoring
to TiO2 surface)
Anionic compounds used for cationic Dyes
IR 783 IR 792 Mercurochrome (MC)
IR 820 IR 1040Bromopyrogallol Red
(BPR)
The number indicates the peak absorption wavelength in nanometers
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Spectral Responsivity
Appl. Phys. Lett., Vol. 85, No. 23, (2004)
0
1
2
3
0.65 0.75 0.85 0.95 1.05Wavelength (μm)
Re
sp
on
siv
ity
(m
A/W
)MC + IR792
BPR + IR820
IR820 + IR1040
BPR + IR1040
IR783
IR820
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1/f-like Noise Characteristics
f
ConsfS
.)(
Spectral power density of noise
Where f is frequency, 0<α<2
α = 0 white noise
α = 1 pink noise (strict 1 / f)
α = 2 brown noise1.E-03
1.E-02
1.E-01
1.E+00
100 1000 10000
f (Hz)
S(f
)(A
2 /Hz) α = 1
α = 0
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Sample Preparation for Noise Measurements
Glass Substrate
Conducting Tin Oxide
TiO2
R = 56 k
18 V
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Noise Measurement Setup
Vacuum
N2, H2O(g)
Heater
Sample
Temp. Sensor
R
Low Noise Pre-Amplifier (SR560)
FT Signal Analyzer(SR785)
PC
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Noise in TiO2 Nanocrystalline Films
0
0
0
0
10 100 1000 10000f (Hz)
S(f
) (A
²/H
z)
10-16
10-25
10-22
10-19
Semicond. Sci. Technol. 20 (2005) L40-L42Infrared Phys. Techn. (2006) In Press, Corrected Proof
TiO2 (N2)
TiO2 (N2 RH >40%)
TiO2 (N2 ,I2 vapor)Adsorbed molecular species such as H2O and I2 can generate 1/f noise
These molecular species can produce electron acceptor state on the TiO2 surface.
It is suggested that the trapping and detrappng of electrons at the surface states is the cause of noise.
α = 1.37
α = 1.25
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0
0
0
0
10 100 1000 10000f (Hz)
S(f
) (A
²/H
z)
10-16
10-25
10-22
10-19
Noise in TiO2+Dye Nanocrystalline Films
TiO2/N3(N2, RH <40%)
TiO2/N3 (N2, RH=70%)
TiO2/BPR
(N2, RH=70%))
TiO2/BPR(N2, RH <40%)
Semicond. Sci. Technol. 20 (2005) L40-L42
TiO2 (N2 RH=70%)TiO2 (N2 ,I2)
The dye coated TiO2 suppresses the 1/f noise
Higher relative humidity can partly desorbs dye from TiO2 surface allowing water adsorption.
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Dye-Sensitized IR Detector Noise
1.E-29
1.E-28
1.E-27
1.E-26
1.E-25
100 1000 10000f (Hz)
S(f
)(A
2 /Hz)
Power spectral density of the dark current noise of the hetrojunction n-TiO2/MC-IR792/p-CuSCN
n-TiO2/MC-IR792/p-CuSCN
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Advantages and Disadvantages
Advantages Disadvantages
1. Cheep
2. Low noise
3. Fully Solid State
4. Detection Wavelength Range Can be change using suitable Dye
5. Detection limits can be extend using Suitable Pair of Dyes.
6. Readily applicable to large area detectors
1. Response Time is slow
2. Long term stability is low
3. Experiment is more important to find a suitable Dyes. (Lower prediction capability)
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GSU HIWIP(Homojunction Interfacial Workfunction Internal Photoemission Detectors)
Absorption is due to free carriers
Barrier formed by Homojunction (p-type)
Δ comes from doping
APL 78, 2241 (2001)
APL 82, 139 (2003)
BarrierUndoped
GaAs
Emitterp+ GaAs
Δ
h+
hν Δ
biased zero bias
p+ GaAs Undoped GaAs
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GSU HEIWIP(HEterojunction Interfacial Workfunction Internal Photoemission Detectors)
Absorption is due to free carriersInterface is sharp (no space charge)
Barrier formed by Heterojunction (p-type)
Δ comes from Al fraction (x) and doping
APL 78, 2241 (2001)
APL 82, 139 (2003)
Δ
h+
hν Δ
biased zero bias
p+ GaAs AlxGa1-xAsBarrier
AlxGa1-xAsEmitterp+ GaAs
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GSU
Spin Split-off Transition Based IR Detectors
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GSUDetector Structure (HE0204)
After processing
Substrate
~1000 A
Metal
p GaAs
AlGaAsp GaAs
p GaAsAlGaAs
p GaAs++
+
+
+
n Periods
Top Contact
Barrier 1250 Å
Emitter 188 Å
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GSU
Split-off Mechanism
IR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow)
Excited holes may escape in split-off band or,
May scatter into the light/heavy hole bands and then escape (Dashed Arrow)
E
k
Heavy Hole Band
Split-off Band
Ef
ΔL/H
ΔSO
Light Hole Band
Conduction Band
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Ek
Light Hole Band
Split-off Band
EF
ΔL/H
escape
Free Carrier Absorption
Light/Heavy Hole Band
Split-off Band
ΔSO
Response Mechanism I
Heavy Hole Band
The photoexcitation process consists of the standardfree carrier absorption.
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Ek
Heavy Hole Band
Split-off Band
EF
ΔL/H Split-off Absorption
Light/Heavy Hole Band
Split-off Band
scattering
ΔSO
Light Hole Band
direct photoabsorption to the split-off band, followed by a scattering to the light/heavy hole band.
Response Mechanism II
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Ek
Heavy Hole Band
Split-off Band
Ef
ΔL/H
escape
Split-off Absorption
Light/Heavy Hole Band
Split-off Band
ΔSO
Light Hole Band
Single indirect photoabsorption into the split-off band.
Response Mechanism III
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Ek
Heavy Hole Band
Split-off Band
Ef
ΔL/H
escapeSplit-off
Absorption
Light/Heavy Hole Band
Split-off Band
scattering
ΔSO
Light Hole Band
Response Mechanism IV
indirect photoabsorption, followed by a scattering event to the light or heavy hole band.
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Split-off Absorption
2 3 4 50.05
0.10
Experiment
2
Abs
orpt
ion
Wavelength (m)
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GSU
Quantum Efficiency of Split-off Detector
2.5 5.0 7.5 10.0 12.5 15.00.00
0.01
0.02Split-off
Response
Free Carrier Response
Qua
ntum
Effi
cien
cy
Wavelength (µm)
Sample 1332
T = 50K
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Split-off Detector Response
0
0.2
0.4
0.6
1 2 3 4 5Wavelength (um)
Re
sp
on
se
(A
/W)
80K
90K
105K
120K
100K
130K
Threshold for mechanism
(III)
Threshold for mechanism
(II / IV)
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GSU
Advantages
• Increased operating Temperature Use of the split-off band provides increased absorption at short wavelengths Increased escape due to high carrier energies Increased gain due to impact ionization from high energy carriers
h+
ip+i
h+
ip+i
h+
ip+i
ΔΔΔ
ESO ESO ESO
Dark Current ~e-
Δ/kT
ΔΔ
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GSU Different material will cover different split-off ranges
Antimonides – 1-2 µm
Arsinides – 3-5 µm
Phosphides – 8-15 µm
Nitrides – 40-60 µm
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GSU
GaSb HIWIP THz Detector
0.05 μm
0.05 μm
5×1018cm-3 p++ GaSb Substrate
2×1018cm-3 p+ emitter
Undoped-GaSb barrier
2×1018cm-3 p+ emitter
5×1018cm-3 p++
2 μm
0.1 μm
Metalcontact
Δ
GaSb
p+ GaSb
p+ GaSb
Energy
EF
EF
Top Contact
Bottom Contact
ΔEV
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GaSb HIWIP THz Detector IV
APPLIED PHYSICS LETTERS 90, 111109 2007
10
10
10
10
-4 -2 0 2 4Voltage (V)
Curre
nt D
ensit
y (A
/cm
²)
-1
-3
-5
GSU-A3T = 10 K
T = 4.9 K
-7
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GSU
GaSb HIWIP THz Detector Response
0
2
4
6
8
10
20 30 40Wavelength (m)
Resp
onsiv
ity (A
/W)
10
10
10
10
10
10
20 80 140 200Wavelength (m)
Resp
onsiv
ity (A
/W)
1
0
-1
-2
-3
-4
3.7 V3.4 V3.0 V2.0 V1.0 V
T = 4.9 KT = 4.9 K (a) (b)
3.0 V2.0 V1.0 V97 μm
15 7Frequency (THz)
10 15 1.5Frequency (THz)
4 2
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Future Studies
• Design optimized split-off band detector operating near room temperature for 3 -5 μm range.
• Use different material system to cover different wavelength range
e.g. Nitrides – 40-60 µm
Phosphides – 8-15 µm
• InGaSb/GaSb HEIWIP design for THz detection
(a) Design single layer HEIWIP detector as first step
(b) Improve performance using multi layer and resonant cavity structures.
(c) Use surface plasmon to enhance detector performance.
(using metal grid pattern on top detector)
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Future Studies
0 100 2000
2
4
240 m
190 m
In0.02
Ga0.98
Sb
GaSb
Res
pons
ivity
(A
/W)
Wavelength (m)
EmitterGaSb
In0.02Ga0.98Sb0.2 μm
2.1 μm
0.7 μm In0.02Ga0.98Sb
GaSb Substrate
GaSb
In0.02Ga0.98Sb
GaSb
0.2 μm
2.1 μm
0.7 μm
GaSb Substrate
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Acknowledgement
Committee Members
• Dr. Unil Perera
• Dr. Kirthi Tennakone
• Dr. Douglas Gies
• Dr. Xiaochun He
• Dr. Vadym M. Apelcov
Committee Members
• Dr. Unil Perera
• Dr. Kirthi Tennakone
• Dr. Douglas Gies
• Dr. Xiaochun He
• Dr. Vadym M. Apelcov
Lab Members
• Dr. Steve Matsick
• Dr. Mohammad Rinzan
• Mr. Aruna Weerasekara
• Mr. Gamini Ariyawansa
• Mr. Ranga Jayasinghe
Lab Members
• Dr. Steve Matsick
• Dr. Mohammad Rinzan
• Mr. Aruna Weerasekara
• Mr. Gamini Ariyawansa
• Mr. Ranga Jayasinghe
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GSU
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Extra stuff
Extra stuff
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GSU
n-type Dye p-type
n-type Dye p-type
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GSU HIWIPHIWIP(Homojunction Interfacial Workfunction Internal Photoemission Detector)
Barrier formed by Homojunction (n-type)
(Δ comes from doping)
n+ doped GaAs
GaAs
Δ
zero bias
e-
in+
ECn
EF
hν
Δ
biased
JAP 77, 915 (1995)
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GSU
E
k
Heavy Hole Band
Split-off Band
Light Hole Band
Conduction Band
E
k
Heavy Hole Band
Split-off Band
Light Hole Band
Conduction Band
Intrinsic (InSb, HgCdTe) Quantum Well
Detector Mechanisms
ESO
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GSU
In this Presentation…
0.1 1 10 100 1000
Wavelength (μm)
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GSU
Modal Results
2 3 4
100
1000
Free Carrier
Abs
orpt
ion
coef
ficie
nt (
cm-1
)
Wavelength (m)
Split-off
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GSU
Split-off MechanismIR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow)
Excited holes may escape in split-off band or, May scatter into the light/heavy hole bands and then escape(Dashed Arrow)
E
k
Heavy Hole Band
Split-off Band
Ef
ΔL/H
ΔSO
Light Hole Band
Conduction Band
• Transition is entirely in hole bands
• Carrier energies are continuous not quantized
• Split-off response is inherently broadband
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GSU
GaSb Absorption
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GSU
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GSU
Dye-Sensitized IR Detector Noise
1E-29
1E-27
1E-25
0 4 8 12f (kHz)
SI(f
) (A
2/H
z)
10-27
10-25
10-29
Power spectral density of the dark current noise of the hetrojunction n-TiO2/MC-IR792/p-CuSCN
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GSU
IR Absorbing Dyes
Anionic Dyes(readily anchor to the TiO2
surface)
Cationic Dyes Anionic compounds used for cationic
DyesIR 783
IR 792
Mercurochrome
IR 820
Bromopyrogallol Red