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Dr. Kitt ReinhardtProgram ManagerAFOSR/RSE
Air Force Research Laboratory
AFOSR
Adaptive Multimodal Sensingand THz-Speed Electronics
Distribution A: Approved for public release; distribution is unlimited. 88ABW-2011-0763
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Research Thrusts
I) Novel UV-IR & S materials, structures and methods(a) New photon material and nanostructure interactions
- photon-material stimulus physics and phenomenology
- novel photon energy transduction methods
- adaptive λ & S filter tuning, optical band-edge manipulation
(b) Innovative hetero-interface formation/integration methods
- interface lattice-strain and defect mitigation- interface energy band-edge alignment manipulation
- interface barrier tunneling and current transport
(c) 3D current transport methods & interconnect schemes
- embedded transport conduits & adaptive conduction methods
- grp II-thru-VI-based transparent (UV-IR) films & electronics
II) THz-Speed electronic materials, device physics & methods(a) novel materials: high- n/p-type III-V’s, multifunctional domain-
engineered oxides, reconfigurable/phase-change, transparentconductive oxides, ao & Eg grading, novel epi & substrate growth
(b) switching constructs & physics: transparent electronics, nano-
enabled (i.e., CNT), ballistic-electron, phonon-manipulation, etc.
20
2x
2
0
2
0
20
2x
2
0
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Transformational Opportunities
Near real-time exquisite C4ISR via breakthrough a) performance-driven sensing ,
b) THz-speed data processing and c) ultrahigh-bandwidth communications
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Sensing Modes
Polarization imaging adds contrastfor enhanced discrimination
Spectral Bands S/M/LWIR SpatialDiscriminat
ionSpectral
Discrimination
intensity image
DOLP
Raw Infrared DOLP
So Intensity S1 0°/90° S2 45°/135°
Spatial (imaging): shape, internal features, context, range profile
Spectral (wavelength): materials characteristics & phenomenology
Polarization: shape, surface roughness, natural vs. manmade
Phase: 3D shape, interferometry
Time (temporal): motion, dynamics, vibration
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Desired „functional‟ breakthroughs(A) epi/sub mismatch strain mitigation methods
(B) epi-dislocation blocking barriers
(C) band-edge alignment manipulation
(D) dynamic bandgap/absorption-edge tuning
(E) dynamic optical absorption-depth tailoring
(F) dynamic wavelength & polarization filtering
(G) novel photon energy transduction methods
(H) 3-D transparent pixel interconnects
Scientific Opportunities & Potential
Enablers(1) carbon nanotubes: (A)-(H)
(2) coaxial nanorods: (A)-(H)(3) core-shell nanocrystals: (A)-(H)(4) Q-dots / wires / wells: (A)-(G)(5) functionalized (1-4) nanostructures: (A)-(H)(6) plasmonic structures & methods: (A)-(G)(7) novel transparent thin-film synthesis: (D)-(H)(8) compliant heterointerface methods: (A)-(C)(9) combinations & integration of (1)-(8
): (A)-(H)
Scientific Opportunities for NovelSensing Structures & Methods
A Multitude of Fundamental Materials Science & Device Physics Challenges
revolutionarycapability
opportunities
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Structured Nanowires for Spectral-Tuned and Multiplexed Sensing
Jimmy Xu (Brown University)
Science: uncover novel-nanowire physics (beyond quantum size effects) in regime ofcorrelated behaviors of coupled e’s, phonons & photons in both short & long couplings
Nano Lett 2010, 10, 3272-3276
diamond nanowire encasedin a low-T graphitic shell
→ tailoring optical absorption
and electron & phonon transportT-junction nanowire with
built-in three terminals
Giant bias-independentPC gain ~ 1000
J. Phys. Chem. C 114, 9634 (2010)
structured Bi2S3 nanowires from simpleto complex, but all highly crystalline
Pd/Au
Pd/Au
Bi2S3 NW
Bi2S3 nanowire grids
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Doping Enhanced Photoresponse in Q-Dot Structures
NEW RESULTS
Experimentally observed-
verified photoresponceenhancement of ~ 30X
due to QD layer doping in
GaAs p/n photodetectors.
Vladimir Mitin (SUNY Buffalo)
Photoresponse vs. Barrier Height
V. Mitin et al., J. Comp. Theor. Nanoscience Vol. 8, pp. 1–4, 2011V. Mitin et al., Nanoscale Research Letters 6, 21 (2011)
+
3/10 RESULTS: QD layer doping → QD charge → potential barrier → suppresses fast electron capture process
Device Dopant
position
Dopant
concentration
Number of
electrons
per QD
Barrier
height,
meV
B44 QD layer 2.7×1011 cm-2 2.4 25
B45 middle of
AlGaAs
layers
2.7×1011 cm-2 2.8 70
B46 modulation
dopping
2.7×1011 cm-2 2.8 60
B52 QD layer 5.4×1011 cm-2 4.7 79
B53 middle of
AlGaAs
layers
5.4×1011 cm-2 6.1 130
B54 middle of
AlGaAs
layers
8.1×1011 cm-2 9 200
Science: Uncover physics governing electron processes in correlated QD structures w/potential barriers
Appl. Phys. Lett., 2009,
Vol. 95, No. 19, pp 173105.
Nanoscience Letters, Vol. 2,
No.2, pp. 129-132, 2010.
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Vladimir Mitin (SUNY Buffalo) and Kim Sablon (U.S. ARL Adelphi)
To date, doped-QD research has produced 1 provisional patent,
10 journal articles, 17 conf. presentations, and 2 Ph.D. dissertations.
Doping Enhanced Photoresponse in Q-DotStructures
-dopedlayer
IR absorption at
4.3 m is drastically
increased due to
pumping by short
wavelength (620nm)
photons.
n-doping of the inter-dot space
suppresses fast electron capture process
strongly enhances IR absorption
Q-dot solar cell structure Sablon et al., submitted to Nano Letters
InAs/GaAs QD Solar Cells with Inter-Dot Doping
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Plasmon-Enhance Photo Absorptionin Novel Device Structures
Yalin Lu (U.S. Air Force Academy)
Science: uncover physics governing plasmonic coupling in novel ordered nanostructures
Y. Lu et al., Nano Lett 2010, 2012–2018
Y. Lu et al., J. Nanophotonics V4, 043515 (2010)Y. Lu et al., Phys. Status Solidi C, 1-3 (2010)
• SCPC enhancement ~ 250%consuming only 42% CIGS
• Net SC PC can reach >10%• GOVERNING MECHANISMS:
- localized plasmonic resonance- waveguiding- antenna effect
Short-Circuit Photo-CurrentDensity for CIGS Solar Cells
• 30% absorption enhancement• insensitive to solar incident
angle (>60°) and polarization• GOVERNING MECHANISMS:
- localized plasmonic resonance- Fabry-Perot cavity resonance- waveguiding
Absorption Enhancementfor a-Si Thin-Films
Embedded Metal Nanograting
Open Metal Nanograting
a-Si
CIGS
plasmon resonance
coherent oscillation of electron cloud
5-200nm
h h
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Q-Dot Resonant Tunneling (RT) Structuresfor Novel V-Tunable Multispectral Sensing
Xuejun Lu (U. Mass Lowell)
integrate multispectral QDIPw/nanowire grid polarizer
3-color QD RT detector band structure
reduce dark current w/o reducing photocurrent
SWIR
MWIR
LWIR
3λs + S single pixel
X. Lu et al., Appl. Phys. Lett. 96, 173105 (2010)
X. Lu et al., Virtual J. of Nanoscale Sci. v.21 (19) (2010)X. Lu et al., Semicond. Sci. Technol. 26 (2011)
zero-bias:no photocurrent
under proper-bias:photocurrent collection
negativedifferentialresistance
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Adaptive 2-λ QD RT Array + Discrete Polarimetry
1. Polarimetric imaging provides enhanced feature detection background clutter detection – can identify front and back sides of target → 3-D
2. Monolithic adaptive-multispectral(modal) enables fused images at collectioneliminates processing needed to register different modes, as they are borsightedreduces processing and transmission bandwidth requirements
monolithic 2-λ (LWIR/MWIR) imager (Xuejun Lu) and fusion algorithms (Erik Blasch - AFRL/RI)
= 00No polarization 450-1350Front 00-900Back = 450
Fused imagemean-mean
LWIR MWIR Fused imagemax-min
Fused imageat collection
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Electronic Materials- novel III-V epitaxy and substrate science- heterointerface stress/defect mitigation
- III-V doping studies
Si
InGaAs~0.5cm2
Novel Transistor Concepts
- III-V‟s: HEMT, HBT, BAVET, …- transparent thin-film FETs- nano-enabled (e.g.,CNT)
- ballistic-electron
Multifunctional Oxides
- domain-engineered multiferroics- novel piezoelectric/ferroelectric
synthesis methods/modeling
Phase-Change-Reconfigurable Matl‟s- non-volatile resistance switching- memristors: hafnium oxides and
chalcogenides & novel deviceconcepts & architectures
Phonon Engineering & Thermal Control- electron mobility enhancement
- nanowire thermoelectrics
- quantum refrigeration
THz-Speed Electronic Materials,Device Physics & Methods
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Novel Heterogenous Materials Integration
Sanjay Krishna (UNM) and Jav Javey (UC Berkeley)
compound semiconductor-on-insulator, dubbed ‘XOI’
Novel method for heterogeneous integration of lattice-mismatched materials
→ important implications for other materials systems and many technology applications
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“Transconductance and Coulomb Blockade Properties of In-plane Grown Carbon Nanotube Field Effect Transistors” E. H.Yang et al., Nanosci. Nanotechnol. Lett. 2, 73-78 (2010).
FET
SET
Elimination of gate hysteresis Graphene FET
"Aperiodic Conductivity Oscillations in Quasi-Ballistic Graphene Heterojunctions", E.H. Yang et
al., Appl. Phys. Lett. 97, 122106 (2010).
Vg(V)
SET operation: Coulomb blockade
CNT FET
Novel Switching Concepts & Physics
E. H. Yang (Stevens Institute)
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Deeply degenerate p-type GaN or InGaN is critical roadblock to achieving RF HBTs motivation is 10-100X power density compared to GaN HEMTs
FUNDAMENTAL PHYSICAL CHALLENGE:
deep ionization levels of Mg results in few holes: less than 1% are activated
APPROACH: Mg-pulsed growth controls surface chemistry → higher conc. of electrically active Mg forms Mott insulator transitions which reduces ionization energy
increased Mg conc. causes deep-level band splitting via Pauli exclusion
Deeply Degenerate p-(In)GaN byNovel Metal Modulated Epitaxy
Alan Doolittle (Georgia Tech)
Record: 52.3% Mg activation efficiency! Record: p = 7.91019 cm-3,
ρ = 0.26 Ω-cm , μ = 0.3 cm2/V-s
A. Doolittle et al., Appl. Phys. Lett. 97, 191902 (2010)
Results: 40X improvement in p
B lli ti D fl ti El t
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Ballistic Deflection ElectronTransistors & Electronics
Martin Margalas (U. Mass at Lowell)
BDT Operation at Room Temp
2DEG BDT Heterostructure
Research Objective: Investigate ballisticelectron transport phenomena in III-V materialnanostructures at room T & THz frequencies.
M. Margala et al., IEEE Transactions on Nanotechnology, pp.723-733, vol. 9, no. 6, Nov 2010M. Margala et al., Solid-State Electronics Journal, vol. 56, pp.120–129, Feb 2011
BDT THz Transfer Function
I di F T
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Indium-Free TransparentThin Film Electronics
Burhan Bayraktaroglu (AFRL/RY) and Dave Look (Wright State U.)
A new transparent electrode material is needed to replace ITO innext generation LCD displays, solar cells, and light-emitting diodes:
the indium supply is limited and controlled by China
ITO is very expensive, and is also highly toxic
Silicon
SiO2GateZnO
SourceDrain
Source
3/10 RESULTS: They have achieved all know world records for thin-film FETs !!
HIGHLY TRANSPARENTand CONDUCTIVE
B. Bayraktaroglu, D. Look et al., Appl. Phys. Lett., 96, 062102 (2010)
APPROACH: leverage expertise & recent scientific breakthroughs in transparent ZnO
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AFM Images of Ga-doped ZnO
Ar
O2
Indium-Free TransparentThin Film Electronics
Near-record low resistivity (1E-4 ohm-cm); low growth temps (RT-200ºC)
1 10 100
1019
1020
1021
Carrier concentration (cm
-3)
Deposition pressure (mTorr)
Argon
Oxygen
1.5 2.0 2.5 3.0 3.5
102
103
Intensity (a.u.)
Energy (eV)
2.0 eV
2.34 eV2.69 eV
3.06 eV
NBE
3.39 eV
O2
Ar
VZn
O2
Ar
SCIENTIFIC CHALLENGE: ZnO deposition in oxygen rich environment results in:
O2 centers at grain-boundaries (GB) trap electrons; compensating acceptor-like defects (VZn)
Annealing in forming gas (FG: 95% Ar/5% H2) is required to passivate defects with hydrogen
→ H2 in FG severely degrades ZnO conductivity and ZnO FET performance
APPROACH: ZnO deposition in Ar to eliminate O2 centers at GB & acceptor-like defects (VZn)
RESULTS: Ga-doping in Ar improved conductivity, stability, & surface morphology RT-deposited GZO in Ar essential for high performance transparent ZnO FETs
First all-ZnO (indium free) high performance transparent FETs
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Highly Conductive Ga-doped ZnO;Theory and Experimental Realization
SCIENTIFIC CHALLENGE: Ga-doped ZnO results in n carrier concentration above 1020 cm-3
which is degenerate, i.e., temperature independent, with n = ND – NA . Up until now, no way toseparately determine ND and NA has been devised.
MAJOR CONTRIBUTIONS: (1) New scattering formulation for degenerate semiconductors;
(2) first PLD growth of ZnO in pure Ar instead of O2 excellent results, even better by annealing
in FG; (3) among best ever resistivities: 1.4 x 10-4
-cm (Appl. Phys. Lett., 97, 072113 (2010)).
New formulas for N D and N A:
1
,,
)(
,
)()(
2
max,max,
exp
max,
C d n
n
T n
n
T
nnN
bdry
ii
ph
ii
t
ii
D
1
,,
)(
,
)()(
2
max,max,
exp
max,
C d n
n
T n
n
T
nnN
bdry
ii
ph
ii
t
ii
A
Agreement betweentheory & experiment
µii,max(n) (APL 96, 062102, 2010)
µbdry(n,d,C) (APL 96, 062102, 2010)
µph(n,T), formula to be publishedµexpt(T), experimental mobility, at any T
d, film thickness
n, carrier concentration, constant with T
C, constant, 3.5 1, determined from µ vs d plot
20
30
40
50
0 100 200 300
Forming-gasanneals
ND
= 0.83e21, NA
= 0.82e20
ND
= 1.1e21, NA
= 1.1e20
ND
= 1.2e21, NA
= 2.2e20
ND
= 1.6e21, NA
= 4.9e20
600 C
500 C
450 C
unann
T (K)
(cm
2/V s)
NEW universal formulas for donor (ND) and acceptor (NA) concentrations in degenerate semiconductors
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DoD Coordination:• ARO: co-fund ASU on novel detector materials science and device effort,
twice served as grant proposal reviewer • ARL: support ARL in-house work in novel Hg-based semiconductor epi-growth (Adelphi),
collaboration with sensors group on doped Q-dot studies• ONR: co-fund THz transistor studies, reliability MURI coordination (now Greg Jessen)
• NRL: good coordination w/NRL - new polarimetry filter research effort in the works
• DARPA: coordination w/Nibir Dhar (sensors); their investments primarily ‘applied’ w/little-to-no 6.1• NSF: generally follow nanoelectronic investments and attend periodic reviews
Conferences/Workshops:• SPIE DSS session organizer/speaker
• SPIE Photonics W. session organizer
•IEEE SISC: session organizer
• IEEE ICSC sponsor
International:• National Cheng Kung University, Taiwan: CNTs
• Semiconductor Physics Institute, Vilnius Lithuania: GaN HEMT studies
• Taras Shevchenko University, Kiev, Ukraine: polarimetry
Coordination/Conferences/International
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Take Aways
Portfolio targets long-term USAF C4ISR capability needs.
Strong thrusts established in multiple fundamental science
challenge areas in solid-state nano materials science,
thin-films synthesis, quantum structures, and multimodal &
multi-discriminate photon-materials/structures interactions.
Good portfolio balance between theoretical and experimental
fundamental research -- most efforts include elements of both.
Excellent progress achieved in quantum structure and deviceinnovation, heterogeneous materials and structures integration,
thin-film transparent films and electronics, and novel detector
and sensing device concepts and methods.