Investigators: Doezema, McCann, Mullen, Murphy, Santos, Shi, Yang (OU); Xie (OSU); Salamo (UA); 6 postdocs/8 graduate students

Partners: Amethyst Research Inc., University of Florida, Humboldt University (Germany), Intel Corp. , Ioffe Technical Institute (Russia), NTT Basic Research Laboratories (Japan), University of Texas at Austin, Tohoku University (Japan), SUNY Albany

Motivation: Future technology needs can be addressed by nanoscaledevices that exploit electron spin, quantum confinement, and ballistic transport.

IRG2: Mesoscopic Narrow Gap Systems

Mesoscopic Device Examples

1

23

4

AuShunt

Au Electrodes

InSb Mesawith

SiNx Cap

b) source draingate

Gate Length~500nm

metal Barrier Narrow-gap semiconductor

Magnetic semiconductor

Magnetic Field Sensor• Working preliminary devices• Room-temperature operation• 30 nm width, diffusive transport• High electron mobility required

Spin Field-Effect Transistor• Studying spin injection and precession• Requires ballistic transport across

interfaces and through channel

Classical Non-classical

Goals of IRG-2

Improved Narrow Gap Materials Improved Narrow Gap Materials MesoscopicMesoscopic Magnetic Field SensorsMagnetic Field SensorsFundamental Studies of Spin Effects in Fundamental Studies of Spin Effects in SemiconductorsSemiconductorsSpin and Ballistic Transport DevicesSpin and Ballistic Transport DevicesInnovative Infrared DevicesInnovative Infrared Devices

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C-SPIN Advantages

Leaders in InSb materials research: MBE, device processing, transport properties Proficiency in optics: Self-induced transparency, coherent optics, ultra-fast pump-probeInventor of Interband Cascade Laser for infrared applications

Mars Science Laboratory (MSL)

CHARACTERIZATION• STM, AFM• TEM, SEM• X-ray Diffraction• FTIR• Hall Effect

Mesoscopic Narrow Gap Systems

MBE GROWTH• InGaAs/AlInAs• InAs/AlSb/GaSb• InSb/AlInSb OPTICS

• Spin Lifetimes• Spin-Orbit Effects• Infrared Devices

TRANSPORT• Quantum Confined Devices• Ballistic Transport Devices• EMR and µ-Hall Devices

FABRICATION• Photolithography• E-beam Lithography• Reactive Ion Etching• Surface Gates

THEORY• Screened Atomic Pseudopotentials

• Spin Transport

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CHARACTERIZATION• Santos (Mishima)• Salamo• Murphy• Doezema

Mesoscopic Narrow Gap Systems

MBE GROWTH• Santos• Salamo• ARI collaborators

OPTICS• Yang• Salamo (Guzun)• McCann• Shi• Doezema

TRANSPORT• Murphy• Salamo (Kunets)• NTT/Tohoku collaborators

FABRICATION• Murphy• NTT/Tohoku collaborators

• Humboldt collaborators• Intel collaborators

THEORY• Mullen• Xie• Ioffe collaborator• Florida collaborator

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Strategy/Progress IRG2Growth

InSbAPL 91, 062106 (2007)

Phys Stat Sol, 2775 (2008)JCG 311, 1972 (2009)

Transport

Hall SensorsJ Mat Sci 19, 776 (2008) IEEE TED 56, 683 (2009)

Spin Lifetime

TheoryOptics

Magneto-opticsAPL 89, 021907 (2006)JVST B24, 2429 (2006)

Springer 119, 213 (2008)

Spin TransportPhysica E 34, 647 (2006)Springer 119, 35 (2008)

Interband Cascade LasersElec Lett 45, 48 (2009)

IV-VIAPL 88, 171111 (2006)

Physica E 39, 120 (2007)

TheoryPRL 101, 046804 (2008)PRB 77, 035327 (2008)PRB 78, 045302 (2008)

Infrared DevicesJAP 101, 114510 (2007)

IEEE PTL 20, 629, (2008) APL 92, 211110 (2008)

I

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B

t212p=3.5x1011cm-2

B (T)

0 2 4 6 8 10 12 14

Ene

rgy

(eV

)

0.00

0.01

0.02

0.03 H10d-H11d H10u-H11u H11d-H12d H11u-H12u

InGaAsAPL 91, 113515 (2007)APL 92, 222904 (2008)APL 94, 013511 (2009

Mesoscopic Narrow Gap Systems

Molecular Beam Molecular Beam EpitaxyEpitaxy of narrow gap materialsof narrow gap materialsSpin related experiments and associated theorySpin related experiments and associated theory–– SpinSpin--relaxation optical measurementsrelaxation optical measurements–– SpinSpin--orbit transport experimentsorbit transport experiments–– Theory and modeling of spinTheory and modeling of spin--orbit devicesorbit devices

NarrowNarrow--gap electronic devicesgap electronic devices–– InGaAsInGaAs--based electronic device structuresbased electronic device structures–– HighHigh--mobility hole systemsmobility hole systems

NarrowNarrow--gap photonic devicesgap photonic devices–– IIIIII--V V InterbandInterband Cascade (IC) LasersCascade (IC) Lasers–– IVIV--VI infrared and thermoelectric applicationsVI infrared and thermoelectric applications

electron m*electron m* gg--factorfactor RashbaRashba coeffcoeff., ., αα

GaAsGaAs 0.067m0.067moo --0.50.5 5.2 e A5.2 e AInIn0.530.53GaGa0.470.47AsAs 0.045m0.045moo --77 65 e A65 e A

InAsInAs 0.023m0.023moo --1515 117 e A117 e AInSbInSb 0.014m0.014moo --5151 523 e A523 e A

III-V Semiconductors

IV-VI Semiconductors

• Band gap in mid-infrared • High thermal conductivity

Electron Mobility and Structural Defects in n-type InSb QWs

4×104

3×104

2×104

0

3.6×109

0

1.2×1046×103

1.8×109

MT density

(/cm)TD density

(/cm2)

Mobility @

RT

(cm2/Vs)

31°Misfit dislocations

54.7°(111) glide plane

1µm

220 Dark-field (DF) X-TEM

Record high mobility for a QW at room temperature when structural defects are minimized.

APL 91, 062106 (2007).

Santos

Mesoscopic Narrow Gap Systems

Molecular Beam Molecular Beam EpitaxyEpitaxy of narrow gap materialsof narrow gap materialsSpin related experiments and associated theorySpin related experiments and associated theory–– SpinSpin--relaxation optical measurementsrelaxation optical measurements–– SpinSpin--orbit transport experimentsorbit transport experiments–– Theory and modeling of spinTheory and modeling of spin--orbit devicesorbit devices

NarrowNarrow--gap electronic devicesgap electronic devices–– InGaAsInGaAs--based electronic device structuresbased electronic device structures–– HighHigh--mobility hole systemsmobility hole systems

NarrowNarrow--gap photonic devicesgap photonic devices–– IIIIII--V V InterbandInterband Cascade (IC) LasersCascade (IC) Lasers–– IVIV--VI infrared and thermoelectric applicationsVI infrared and thermoelectric applications

Spin Orbit Effects

( )2// zkkη±≈ //kzεα±=

Bulk Inversion Asymmetry Structural Inversion Asymmetry

Dresselhaussplitting

Rashbasplitting

ηη αα

GaAsGaAs 27.6 27.6 eVeV ÅÅ33 5.2 e 5.2 e ÅÅ22

InAsInAs 27.2 27.2 eVeV ÅÅ33 117 e 117 e ÅÅ22

InSbInSb 760 760 eVeV ÅÅ33 523 e 523 e ÅÅ22

Large effects predicted in narrow gap materials• Spin splitting at zero magnetic field• Spin precession• Spin-dependent ballistic trajectories

Optical Spin MeasurementsSpin TransportNMR StudiesTheory

Spin Related Experiments and Theory

Salamo (UA)Murphy, Santos, Mullen (OU)Xie (OSU)Golub (Russia)NTT Basic Research Laboratories (Japan) Tohoku University (Japan)

Optical Measurements of Spin Relaxation Salamo, Murphy, Santos

MechanismsElliot-Yafet (spin orbit)Dyakanov-Perel (inversion asymmetry)Bir-Aranov-Pikus (spin exchange with holes)Hyperfine interactions

State of the FieldGaAs extensively studiedInAs studiedInSb limited studies

Optical Measurements of Spin Relaxation Salamo, Murphy, Santos

Optical Measurements of Spin Relaxation Salamo, Murphy, Santos

Future work: Quantum Wells Confinement Energy, Confinement Asymmetry

Bulk InSb

Elliot-Yafetmechanismresponsible for spin relaxation in bulk InSb

Spin Transport MeasurementsMurphy, Santos

First observation of current focusing peaks in InSb heterostructures.

Physica E 34, 647 (2006).

Spin Transport MeasurementsMurphy, Santos

B┴B║

BT

θDoublet is related to spin.

Current Effort and Future Work: • Improved Gating with NanoTech UCSB & Penn State NanoFab• Spin Interferometers (Rings and Ring Arrays)

Physica E 34, 647 (2006).

Weak Anti-Localization MeasurementsMurphy, Santos, Golub

Good agreement with theoretical predicted values of spin-orbit coupling in InSb.

Future: study WAL as a function of gate voltage and applied strain.

Springer Proc. Phys. 119, 35 (2008).

Designing Spin-Orbit CouplingMullen, Murphy, Santos

SYMMETRIC ASYMMETRIC

Future Work: Design structure to maximize change in S-O with applied gate voltage.

Spin and Spin Hall TheoryXie

Proposed Device• Non-uniform Rashba effect • Spin interference• Current predicted to be ~10% spin

polarized• Device not yet realized

Spin Nernst EffectPersistent Spin Currents

PRB 77, 035327 (2008)PRB 78, 045302 (2008)

Mesoscopic Narrow Gap Systems

Molecular Beam Molecular Beam EpitaxyEpitaxy of narrow gap materialsof narrow gap materialsSpin related experiments and associated theorySpin related experiments and associated theory–– SpinSpin--relaxation optical measurementsrelaxation optical measurements–– SpinSpin--orbit transport experimentsorbit transport experiments–– Theory and modeling of spinTheory and modeling of spin--orbit devicesorbit devices

NarrowNarrow--gap electronic devicesgap electronic devices–– InGaAsInGaAs--based electronic device structuresbased electronic device structures–– HighHigh--mobility hole systemsmobility hole systems

NarrowNarrow--gap photonic devicesgap photonic devices–– IIIIII--V V InterbandInterband Cascade (IC) LasersCascade (IC) Lasers–– IVIV--VI infrared and thermoelectric applicationsVI infrared and thermoelectric applications

MBE growth (C‐SPIN, Santos)

InxGa1‐xAs/InxAl1‐xAs MBE

Epilayer characterization(C‐SPIN, Santos)

HRXRD, Hall effect, AFM, TEM

Epilayers for high‐κ integration (UT Austin, Jack Lee)

HfO2

Epilayers for high‐κ integration (SUNY Albany, Serge Oktyabrsky)

ZrO2 

Gated Narrow-Gap InxGa1-xAs QWs

Epilayers for high‐κ integration (Penn State/Cornell, Darrell Schlom)

LaAlO3

Scanning Tunneling Microscopy/Spectroscopy

(UC San Diego, Andrew Kummel)Ga2O, and  In2O

8 journal articles since 2007 on ZrO2, HfO2, LaAlO3 on InxGa1-xAs

Challenges for III-V transistors• Stable & reliable gate dielectric• Integration with Si substrates• p-channel III-V FET for CMOS

Effective Mass of Holes in InSb QW

Cyclotron Resonance at 4.2K

t212b (p=3.5x1011cm-2)

Frequency (cm-1)

20 40 60 80 100 120

T(B

)/T(0

)

1.0

1.5

2.0

2.5

3.0

2.0T

7.0T

6.0T

5.0T

4.0T

3.0T

6.5T

5.5T

4.5T

3.5T

2.5T

Quantum well mh*

GaAs 0.5 mo

In0.20Ga0.80As 0.19 mo

InSb ≥0.04 mo

p (cm-2) mh*

2x1011 0.04 mo

3x1011 0.06 mo

5x1011 0.09mo

p‐FET

n‐FET

• Low-T mobility (~50,000 cm2/Vs) consistent with effective mass

• 300K mobility (700 cm2/Vs) much lower than expected

Doezema, Santos, Stanton

APS 2009

p-type InSb Quantum Well

µH at 300K(cm2/Vs)

Reference

In0.2Ga0.8As 260 R.T. Hsu et al., Appl. Phys. Lett. 66, 2864 (1995).

In0.53Ga0.48As 265 Y-J. Chen and D. Pavlidis, IEEE Trans. Elec. Dev. 39,

466 (1992).

In0.82Ga0.18As 295 A.M. Kusters et al., IEEE Trans. Elec. Dev. 40, 2164

(1993).

InSb 700 M. Edirisooriya et al., J. Cryst. Growth 311, 1972

(2009).

In0.4Ga0.6Sb 1500 B.R. Bennett et al., Appl. Phys. Lett. 91, 042104

(2007).

Ge 3100 M. Myronov, Appl. Phys. Lett. 91, 082108 (2007).

Al0.10In0.90Sb

Al0.10In0.90Sb

Al0.20In0.80Sb

Al0.20In0.80Sb

Al0.20In0.80Sb

15nm InSb well

Buffer Layer

GaAs (001) substrate

30 nm

20 nm

Be δ‐doping

Be δ‐doping

First realization of remotely-doped p-type InSb QWs.

Santos

Integration of InSb n-FET and Ge p-FET

BOX = Buried OxideBOX

Si

BOX

Si

GeOIn-FET p-FETGeInSb

n-FET p-FETGeInSb

Si substrateGe substrate

Ge substrate type GeOI / Si substrate typeAmethyst Research Inc.

340 360 380 400 420 4400

200

400

600

800

InSb epilayer: 2.0 µm

Growth temperature (0C)

X

-ray

rock

ing

curv

e w

idth

(arc

sec

)

two-step growth

direct growth

0 50 100 150 200 250 3000

5,000

10,000

15,000

20,000

25,000

Car

rier d

ensi

ty, n

(x10

12 c

m-2)

Hal

l mob

ility

, µ (c

m2 /V

-s)

Temperature (K)

0

2

4

6

8

p-type

n-type

Santos

APS 2009

Mesoscopic Narrow Gap Systems

Molecular Beam Molecular Beam EpitaxyEpitaxy of narrow gap materialsof narrow gap materialsSpin related experiments and associated theorySpin related experiments and associated theory–– SpinSpin--relaxation optical measurementsrelaxation optical measurements–– SpinSpin--orbit transport experimentsorbit transport experiments–– Theory and modeling of spinTheory and modeling of spin--orbit devicesorbit devices

NarrowNarrow--gap electronic devicesgap electronic devices–– InGaAsInGaAs--based electronic device structuresbased electronic device structures–– HighHigh--mobility hole systemsmobility hole systems

NarrowNarrow--gap photonic devicesgap photonic devices–– IIIIII--V V InterbandInterband Cascade (IC) LasersCascade (IC) Lasers–– IVIV--VI infrared and thermoelectric applicationsVI infrared and thermoelectric applications

Interband Cascade (IC) Laser

hv

hv

InAs/Al(In)Sbmultilayers AlSb

InAsGaInSbAlSb

AlSbGaSb

InAs/Al(In)Sbmultilayerscascade process —

»high efficiency, large output power, uniform injection over every stage, low carrier concentration, thus lower loss

interband transition —»circumvents fast phonon scattering

quantum engineering at sub-nanometer scale and Sb-based type-II QW system

»suppresses non-radiative Auger losses»allows for wide wavelength tailoring range»excellent carrier confinement because of

band-gap blocking feature

Low threshold current, high efficiency, high output power mid-IR lasers

type-II brokengap alignment

many photons per electronhv hv

hvhv

hvhv

hv

Cascading

Ee

Yang, Johnson, Santos

Preliminary Results of InterbandCascade Lasers

5600 5650 5700 5750 5800 5850 59000.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

(a.u

.)

Wavelength (nm)

82K136mA

100K193mA

120K301mA

140K515mA

150K696mA

CW

150µmx1.86mm

A broad-area (150µm x 1.9mm) device lased in continuous wave (cw) mode up to 150 K near 6 µm, the longest attained, to date, for III-V interband diode lasers.

Electron. Lett. 45, 48 (2009)

Latest Results

11-stage IC laserJth~82 A/cm2, Vth~2.3V, at 84K

7.20 7.25 7.30 7.35 7.40 7.45

100K670mA

100K424mA

90K298mA

Inte

nsity

(a.u

.)

Wavelength (µm)

84K234mA

CW

118K1000mA

150µmx1.9mm

Lower threshold current density and operating voltageLasing wavelength ~7.4 µmLonger wavelengths possible

Where are we?

III-V Sb-based mid-IR diode lasersreported in literature and

3.0 3.5 4.0 4.5 5.0 5.5 6.00

100

200

300

400

JJ

ICL pulsed, cwtype-II pulsed, cwtype-I pulsed, cw

Max

imum

tem

pera

ture

(K)

Wavelength (µm)

0.4 0.3

NJ

NN

N

N

N

JJ

J

J

J

JJ

J

J

J

J

JJ

J

J

J

J

JJ

J

J

J

J

JJ

N

J

J

J

JJ

J

J

J

J

J

J

Photon energy (eV)

OU

J - JPL

N-NRL

OU- University of Oklahoma

Device fabrication and package are in a preliminary stage for ICLs

OU

Our latest lasers operate up to 121 K near 7.4 µm, now the longest attained to date, for III-V interband cascade lasers.

PbSe Quantum Wires for Thermoelectric Applications

• CaF2 growth on Si (110) adopts a ridge-groove morphology• Subsequent growth of PbSe produces quasi-one-dimensional structures

indicated by a 200 meV blue shift in PL • Improved thermoelectric properties predicted, based on enhanced electrical

conductivity, but reduced thermal conductivity, along wires.– TE figure of merit, ZT ∝ σ/κ, σ and κ, electrical and thermal conductivities, resp.

CaFCaF22 200 nm200 nm

[110][110]

McCann Ridge-groove CaF2 structure and subsequent PbSe growth.

Grayscale: 95 nmGrayscale: 95 nm

200 nm200 nm2 ML 2 ML PbSePbSe

[110][110]

PbSePbSeQWRQWR

AFM of AFM of 2 ML 2 ML PbSePbSe

200 nm200 nm

[110][110]

CaFCaF22

PbSe Micro/ Nanostructures

APL 88, 171111 (2006).

SEM image and PL of a freestanding MQW microtube. Diameter 600, length 5 mm.

SEM images and PL of PbSemicro-rods.

4 µm

Physica E 39, 120 (2007).

4 µm

PbSePbSe layerslayers

BaFBaF 22 layerlayer

ShiStrain in MQW causes rolling of PbSe when BaF2 layer is removed in water.

PbSebulk PbSe

bulk

IRG2: Mesoscopic Narrow Gap Systems

Comprehensive expertise: MBE, characterization, Comprehensive expertise: MBE, characterization, fabrication, transport and optical experiments, theoryfabrication, transport and optical experiments, theoryFundamental and technologically motivated studiesFundamental and technologically motivated studiesDevices exploit high mobility, quantum confinement, Devices exploit high mobility, quantum confinement, ballistic and spin effectsballistic and spin effects

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I

GG

C

B

Strategy/Progress IRG2Growth

InSbAPL 91, 062106 (2007)

Phys Stat Sol, 2775 (2008)JCG 311, 1972 (2009)

Transport

Hall SensorsJ Mat Sci 19, 776 (2008) IEEE TED 56, 683 (2009)

Spin Lifetime

TheoryOptics

Magneto-opticsAPL 89, 021907 (2006)JVST B24, 2429 (2006)

Springer 119, 213 (2008)

Spin TransportPhysica E 34, 647 (2006)Springer 119, 35 (2008)

Interband Cascade LasersElec Lett 45, 48 (2009)

IV-VIAPL 88, 171111 (2006)

Physica E 39, 120 (2007)

TheoryPRL 101, 046804 (2008)PRB 77, 035327 (2008)PRB 78, 045302 (2008)

Infrared DevicesJAP 101, 114510 (2007)

IEEE PTL 20, 629, (2008) APL 92, 211110 (2008)

I

GG

C

B

I

GG

C

B

t212p=3.5x1011cm-2

B (T)

0 2 4 6 8 10 12 14

Ene

rgy

(eV

)

0.00

0.01

0.02

0.03 H10d-H11d H10u-H11u H11d-H12d H11u-H12u

InGaAsAPL 91, 113515 (2007)APL 92, 222904 (2008)APL 94, 013511 (2009