This document provides an overview of Jim Hwang's Adaptive Multimode Sensing portfolio at AFOSR. The portfolio focuses on three main areas: 1) adaptive multimode sensing with an emphasis on tunable detectors that can detect properties like polarization and phase in addition to intensity and color, 2) novel infrared sensors using quantum dots, nanowires, and other novel materials and structures with the main challenge being dark current, and 3) solar cells, thermoelectric coolers, and other areas that will be deemphasized to focus the reducing budget. Several research projects within these areas are briefly described that aim to shorten the time from sensing to action and avoid being overwhelmed by data.

1. 1Distribution A: Approved for public release; distribution is unlimited
Integrity  Service  Excellence
Adaptive
Multimode
Sensing
Date: 07 03 2013
Jim Hwang
Program Officer
AFOSR/RTD
Air Force Research Laboratory

2. 2Distribution A: Approved for public release; distribution is unlimited
2013 AFOSR SPRING REVIEW
3001B PORTFOLIO OVERVIEW
NAME: Jim Hwang
BRIEF DESCRIPTION OF PORTFOLIO: Adaptive Multimode Sensing
LIST SUB-AREAS IN PORTFOLIO:
I. Adaptive Multimode Sensing – Emphasize tunable
detectors and different detection modes such as
polarization and phase (in addition to intensity and
color). Main challenge: phase detection.
II. Novel Infrared Sensors – Emphasize novel materials and
structures such as quantum dots, nano-wires, type-II
superlattices, and 3D integration. Main challenge: dark
current.
III.Solar Cells, Thermoelectric Coolers & Others –
Deemphasize to focus portfolio with reducing budget.

3. 3Distribution A: Approved for public release; distribution is unlimited
Motivation
Shorten time from sense to kill; avoid drowning in data

4. 4Distribution A: Approved for public release; distribution is unlimited
-2 V
S.I. GaAs Substrate
LWIR AlGaAs/GaAs QWIP
NIR AlGaAs/GaAs PIN
-2 V
S.I. GaAs Substrate
LWIR AlGaAs/GaAs QWIP
NIR AlGaAs/GaAs PIN
Near IR LWIR
77 K
3-Color detector
demonstrated, too.
Optically-Switched 2-Color Infrared Detector
Yong-Hang Zhang (Arizona State) & Elizabeth Steenbergen (AFRL/RXAN)

5. 5Distribution A: Approved for public release; distribution is unlimited
Speed/Sensitivity Trade-Off of IR Detectors
Vladimir Mitin (Buffalo) & Andrei Sergeev (Buffalo)
Potential barriers around
charged InAs quantum dots
(QDs) in GaAs prevents
recombination and
prolongs electron lifetime
Charged QDs strongly
enhance IR response of
photo-detectors/solar cells
p+ GaAs
InAs QDs
n+ GaAs
InAs QDs
n+ GaAs
n+ GaAs

6. 6Distribution A: Approved for public release; distribution is unlimited
Electrically Switchable Plasmonic Polarizers
Xuejun Lu (Mass-Lowell)
Field distribution (resonance
wavelength) can be switched by
electrically biasing the polarizer
RectangularArrayof
AuPlasmonicPolarizers

7. 7Distribution A: Approved for public release; distribution is unlimited
Spectral-Polarization Imaging
Viktor Gruev (Washington, St. Louis)
Color Filters
Angle of Polarization Image
SEM of Al Nanowires
Si
Si
Cone
Polarization
Filter

8. 8Distribution A: Approved for public release; distribution is unlimited
0 100 200 300 400 500 600 700
0.0
0.1
0.2
0.3
0.4
Photocurrent(µA)
Time(ns)
x0.3
PbS QD
2 nm
(111)
planes
(111)
planes
0.004 0.006 0.008 0.010 0.012 0.014
1E-5
1E-4
1E-3
0.01
0.1
250 167 125 100 83 71
1E-1
QDDecayRate(ns-1
)
1E-2
T (K)
1/T ( K-1)
Non-radiative
Energy Transfer
Si
Non-radiative Energy Transfer from Quantum Dots
Anupam Madhukar (S. Cal.), M. Mahalingam (RXAN) & G. Brown (RXAN)
Controlled energy/charge transfer between
colloidal nanostructures and conventional semiconductors
Substrate
QD
10−1
10−2
10−3
10−4
10−5
PhotoluminescenceDecay(/ns)
Si

9. 9Distribution A: Approved for public release; distribution is unlimited
Crystalline Bismuth Nanowire
Jimmy Xu (Brown)
Bi Pt
Bi Pt
IR/THz
Detector
• Bi: only known natural
negative index material
@ 60um or 5THz
• Bi oxides easily
• 1st Bi/Pt heterojunction
successfully grown

10. 10Distribution A: Approved for public release; distribution is unlimited
InAs/GaSb Type II Superlattices
Sanjay Krishna (New Mexico), Vincent Cowan (RVSS), Christian Morath (RVSS) & John Hubbs (RVSS)
Collaboration
with Raytheon
Vision Systems
• Type II superlattices with
antimonides barriers can
compete with HgCdTe for
infrared sensing
• Strong interests from
AFRL (RX, RY, RV), Army
NVL, MDA and DARPA
• Enhanced multimodal
functionality (color,
polarization, dynamic
range, phase) through
integration with
metamaterials
Mid-IR
Response
@ 420 K!
GaSb
InAs
EC
EV

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Single-Crystal Semimetal/Semiconductor Nano-Composites
Chris Palmstrøm (UCSB) & Kurt Eyink (AFRL/RXAN)
IncreasingErSbcomposition[001]
ρ
˔ ρ//
{110}
GaSb
ErSb
GaSb
ErSb
GaSb(ErSb)x(GaSb)1-x
(Semimetal) (Semiconductor)
•ErSb/GaSb nano-
composites grown by
molecular beam
epitaxy
•Buried conductive
layers for multicolor
infrared detectors
•THz polarizers
embedded in III-V
heterostructures

12. 12Distribution A: Approved for public release; distribution is unlimited
Funding Trend
I. Adaptive Multimode Sensing – Emphasize
tunable detectors and different detection modes
such as polarization and phase (in addition to intensity
and color). Main challenge: phase detection.
II. Novel Infrared Sensors – Emphasize novel
materials and structures such as quantum dots, nano-
wires, type-II superlattices, and 3D integration. Main
challenge: dark current.
III.Solar Cells, Thermoelectric Coolers & Others –
Deemphasize to focus portfolio with reducing budget.