2. Reinhardt - Adaptive Multimodal

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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



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



Transformational Opportunities

Near real-time exquisite C4ISR via breakthrough a) performance-driven sensing ,

b) THz-speed data processing and c) ultrahigh-bandwidth communications



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



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



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



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.



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



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



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



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



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



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



“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)



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



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



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



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



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



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



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.

2. Reinhardt - Adaptive Multimodal

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