High Operating Temperature (HOT) Split-off Band IR Detectors

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High Operating Temperature (HOT) Split-off Band
IR Detectors
Viraj Jayaweera
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Outline

• Introduction
• IR Range, Applications, Types of IR
  detectors
• Interfacial Workfunction Internal Photoemission
  (IWIP) Detectors
• Detector Structure, HIWIP HEWIP Mechanisms
• Detector Measurements and Characterization
• Split-off Band Detectors
• Possible Material Systems to Extend Spectral
  Range
• Conclusion and Future Studies

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Discovery of Infrared
Sir Frederick William Herschel (1738-1822)
musician and an astronomer famous for his
discovery of the planet Uranus in 1781 Discovered
calorific rays in 1800 later renamed as
Infrared rays
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What is Infrared (IR) ? (the prefix infra means
below)
The electromagnetic spectrum includes gamma rays,
X-rays, ultraviolet, visible, infrared,
microwaves, and radio waves. The only difference
between these different types of radiation is
their wavelength or frequency.
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Infrared is usually divided into 3 spectral
regions
Micro wave
Visible
near-IR
mid-IR
Far-IR
0.8 5 ?m 5 - 40 ?m 40 - 250 ?m
Cant see (human eye)
? 0.75 ?m
Some animals can "see" in the infrared. For
example, snakes in the pit viper family (e.g.
rattlesnakes) have sensory "pits," which are used
to detect infrared light. This allows the snake
to find warm-blooded animals.
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This is the radiation produced by the motion of
atoms and molecules in an object. Any object
which has a temperature above absolute zero (0 K)
radiates infrared.
person holding burning match
Cat
Infrared image of Orion
Landing space shuttle
Application biophysics, communication, remote
sensing, medical imaging, security and
astrophysics.
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Human vehicle at total darkness thermal image
in whitehot mode
same image in Blackhot mode
Human Suspect climbing over fence at 249 AM in
total darkness
Suspect attempting to burglarize vehicle at 147
AM in total darkness.
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Types of IR Detector
IR Detectors
Pyroelectric Detectors
Photon Detectors
Thermal Detectors
Photo Conductive
Photo Conductive
Photovoltaic
Bolometer
Thermopile
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Real Detector
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Structure of the Interfacial Workfunction
Internal Photoemission Detector.
(photo conductive type)
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HIWIP (Homojunction Interfacial Workfunction
Internal Photoemission Detector)
i
n
GaAs
n doped GaAs
e-
h?
?
?
EF
ECn
zero bias
biased
Barrier formed by Homojunction (n-type)
(Interfacial Workfunction ? comes from doping)
JAP 77, 915 (1995)
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HEIWIP (HEterojunction Interfacial Workfunction
Internal Photoemission Detector)
i
n
AlGaAs
n GaAs
e-
h?
?
?
biased
zero bias
Barrier formed by Heterojunction
(n-type) Interfacial Workfunction ? comes from
Al fraction and doping (? ?d ?x)
Absorption is due to free carriers Interface is
sharp (no space charge)
APL 78, 2241 (2001) APL 82, 139 (2003)
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HEIWIP (HEterojunction Interfacial Workfunction
Internal Photoemission Detector)
AlGaAs
p GaAs
?
zero bias
Barrier formed by Heterojunction
(p-type) Interfacial Workfunction ? comes from Al
fraction and doping (? ?d ?x)
Absorption is due to free carriers Interface is
sharp (no space charge)
APL 78, 2241 (2001) APL 82, 139 (2003)
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Measurements and Characterization
(IVT) Current Voltage Temperature measurements

• Using IVT measurements
• Uniformity of sample (dark current density vs.
  voltage plot)
• Dark Current Variation with bias Voltage and
  Temperature
• Background Limited Infrared Photon detector
  (BLIP) Temperature
• Interfacial Workfunction (?) (slope of
  ln(I/T1.5) vs. 1/T plot)

He closed-cycle refrigerator head
Vacuum
Sample
Cold finger
Radiation shield
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Measurements and Characterization
Spectral Response
Source
Moving mirror
Sample
Beam splitter
Fixed mirror
FTIR Spectrometer
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Detector Output
Responsivity (R)
Radiation Input
of electrons produced
Quantum Efficiency (?)
of photons insident
Radiant flux necessary to give an output signal
equal to the r.m.s. noise output of the detector
Noise Equivalent Power (NEP)
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Detectivity (D)
NEP
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Split-off Response
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Split-off Response of the Detector HE0204 Under
Different Temperatures
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• Detector mechanism consisting of three processes
• Photoabsorption. (produces excited carriers)
• Carrier escape.
• Sweep out and collection of the escaped carriers.

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Response Mechanism I
Light/Heavy Hole Band
E
k
Ef
?L/H
escape
Free Carrier Absorption
Heavy Hole Band
Light Hole Band
?SO
Split-off Band
Split-off Band
The photoexcitation process consists of the
standard free carrier absorption.
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Response Mechanism II
Light/Heavy Hole Band
E
k
Ef
?L/H
Split-off Absorption
Heavy Hole Band
escape
Light Hole Band
scattering
?SO
Split-off Band
Split-off Band
direct photoabsorption to the split-off band,
followed by a scattering to the light/heavy hole
band.
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Response Mechanism III
Light/Heavy Hole Band
E
k
Ef
?L/H
Split-off Absorption
Heavy Hole Band
Light Hole Band
?SO
Split-off Band
Split-off Band
escape
Single indirect photoabsorption into the
split-off band.
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Response Mechanism IV
Light/Heavy Hole Band
E
k
Ef
?L/H
Split-off Absorption
Heavy Hole Band
escape
Light Hole Band
scattering
?SO
Split-off Band
Split-off Band
indirect photoabsorption, followed by a
scattering event to the light or heavy hole band.
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The Split-off Band Offset Energy for Different
Materials
Material ?SO (meV) ?SO (µm) Elh (meV) Eso (meV)
InN 3 410 -790 -793
GaN 20 62 -1840 -1860
AlN 19 65 -2640 -2660
InP 108 11 -140 -248
GaP 80 16 -470 -550
AlP 70 18 -940 -1010
InAs 390 3.2 210 -180
GaAs 340 3.6 0 -340
AlAs 280 4.4 -530 -810
The energies of the light/heavy hole band (Elh)
and the split-off hole band (ESO) relative to the
valance band maximum of GaAs.
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Conclusion and Future Studies

• High Operating Temperature
• The devices tested with a threshold of 20 µm
  showed a maximum operating temperature of 130 K.
  By reducing the threshold to 5 µm, the operating
  temperature should be increased to 300 K with D
  of 5109 Jones.
• Increase Quantum efficiency
• Absorption efficiency can be increase by
• Increasing the no of emitter layers
• Increasing the doping to the maximum possible
  value
• Device Design for a 15 µm Detector Operating at
  200K
• Device will based on p-doped GaP emitters and
  undoped AlGaP barriers.

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Thank You