1

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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Spin Split-off Transition Based IR Detectors

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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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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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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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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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Antimonides – 1-2 µm

Arsinides – 3-5 µm

Phosphides – 8-15 µm

Nitrides – 40-60 µm

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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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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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Extra stuff

Extra stuff

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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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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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In this Presentation…

0.1 1 10 100 1000

Wavelength (μm)

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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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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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GaSb Absorption

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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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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