university of salamanca, spain - fapesp of salamanca, spain ... thz radiation can be used to...

Nanodevices for THz Applications

Tomás González University of Salamanca, Spain

Research Group on

Semiconductor Devices

T. González - Nanodevices for THz Applications December 12, 2012

THz Nanodevices at USAL

Research Group on Semiconductor Devices

- Modeling of nanodevices for THz applications

- Design of optimized structures (feedback to technology)

THz Laboratory

- Detection and emission of THz radiation from plasma wave nanodevices

- Time-domain spectroscopy and imaging in the THz range

http://campus.usal.es/~gelec/ CONTACT: Prof. Tomás González ([email protected])

Monte Carlo simulation of high-frequency nanodevices

Characterization Laboratory (DC-GHz) Semiconductor Nanodevices for Room Temperature

THz Emission and Detection - http://www.roothz.eu/

Coordinator of the FP7 STREP Project ROOTHz (FP7-243845)

GaN diodes InGaAs/InAlAs diode

100nm

Advanced Si MOSFETs (FP6 project METAMOS)

InGaAs/InAlAs, InAs/AlSb and GaN/AlGaN HEMTs

InGaAs based THz ballistic nanodevices (FP5 project NANOTERA )

TBJs YBJs MUX/DEMUX SSDs

Staff: 8 permanent researchers, 3 post-doc, 2 students

Collaborations with several EU (IEMN, Chalmers, Manchester, Montpellier, etc.) and USA Labs. (Rochester)

RESEARCH LINES


http://www.roothz.eu/

EQUIPMENT

Computer Clusters

Keithley 4200: DC and pulsed measurements (Keithley 4225)

Probe station (Cascade M150)

VNA Agilent PNA-X: RF measurements up to 43.5 GHz


Doubly interdigitated grating

gates in III-V HEMT Strained Si/SiGe n-MODFET

THz detectors based on Graphene transistors

A glimpse of the considered structures:

THz Laboratory

Contact: Dr. Yahya Meziani ([email protected])

Plasma-wave nanodevices

Si/SiGe MODFETs

used as sensors in

THz signals detection

Si/SiGe MODFETs

used as sensors in

THz imaging

THz Laboratory

Facilities

Terahertz Spectroscopy System

THz-Time Domain Spectroscopy System: EKSPLA

Spectrometer+Ti:Sapphire Laser (Spectra-Physics)

THz imaging: Gunn Diode at 0.2TH + frequency tripler

Probestation

Cascade Summit 11000B manual probestation with

FemtoGuard® and PurelineTM technologies (200mm-chuck)

+ Agilent B1500 (4 SMUs, 1 multifreq CMU and 1 WG/FMU

THz Laboratory


Introduction. Importance of THz

ROOTHz Project

Self Switching Diodes (SSDs)

Conclusions / Perspectives

Outline

Outline


1 THz = 1012 Hz

THz range (100 GHz to 10 THz)

(300 GHz to 3 THz, 1 - 0.1 mm)

The THz Band


Image of sea surface temperature (European Space Agency)

THz radiation can penetrate poor weather, dust and smoke far better than infrared or visible systems.

Satellite Telemetry

Aeronautics: guidance and landing

Potential applications


THz radiation can penetrate organic materials without ionizing

Readily absorbed by water: distinguish between materials with varying water content

Medical imaging

Courtesy of Teraview Courtesy of Teraview

Skin Cancer Detection

Potential applications: medical diagnosis


THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls

Potential applications: security


Non-destructive testing: integrated circuit package inspection

Courtesy of Teraview


Potential applications: testing



THz radiation can penetrate organic materials without ionizing

Weapon or Explosive Detection (metallic or non metallic)

Courtesy of Qinetiq Courtesy of Thruvision Courtesy of Qinetiq




Full-body security screening, body scanners


Passive Detection - no THz source is needed


THz radiation can be used to identify spectral fingerprints of explosives, narcotics, or active pharmaceutical ingredients

THz Spectroscopy

Potential applications: spectroscopy

Driving force of THz technology so far: spectroscopy, imaging, sensing

Active Detection - THz sources are needed (narrow or broadband)


Potential applications: communications


Evolving THz market


The THz gap

ELECTRONICS PHOTONICS THz Gap

All-optical sources

•Mixing lasers with close frequencies

•Excitation of semiconductors or

superconductors with fs laser pulses

•Quantum cascade lasers

All-electronic sources

• Gunn diodes + frequency multipliers (Schottky diodes)

Bulky and expensive equipment

Useful for spectroscopy and sensing, but not for communications

Very low power in the THz range

Backward wave oscillators - BWOs (vacuum electronic device)


The THz Gap

Quantum cascade lasers (QCL)

QCL at cryogenic T

Frequency multipliers

_ Other electronic devices: amplifiers, RTDs, IMPATT and Gunn diodes

500 GHz – 5 THz

Source: T. H. Crowe, W. L. Bishop, D. W. Porterfield, J. L. Hesler, and R. M. Weikle

“Opening the Terahertz Window with Integrated Diode Circuits”

IEEE J. Solid-State Circuits 40, 2104 (2005)

Signal generation at THz frequencies

PROBLEM Lack of a compact,

room-temperature, high-power, semiconductor

tunable source

Semiconductor Nanodevices for

Room Temperature THz

Emission and Detection

(ROOTHz Project)

The THz gap



ROOTHz Project



Outline

Outline


• Funded under: 7th FWP (Seventh Framework Programme)

• Area: FET Open (ICT-2007.8.0)

• Project Reference: 243845

• Total cost: 2.1 M€

• EU contribution: 1.57 M€

• Execution: from 1st January 2010 to 30th June 2013

• Duration: 42 months

• Website: www.roothz.eu

Semiconductor Nanodevices for Room

Temperature THz Emission and Detection

(ROOTHz Project)

The Project


C. Gaquiere

Institut d’Electronique Microélectronique

et de Nanotechnologie, Lille, France

A.M. Song

The University of Manchester

Manchester, UK

J. Grahn

Chalmers University of Technology

Gothenburg, Sweden

Coordinator: J. Mateos

University of Salamanca

Salamanca, Spain

Partners



Slot Diodes (Ungated HEMTs)

Barrier

Ohmic

Contact

Ohmic

Contact

Buffer

Channel

Cap LayerTop View

CurrentInsulating Trenches

Co

ntact

Co

ntact

Narrow Bandgap

Semiconductors (NBG):

InGaAs/AlInAs

InAs/AlSb

Wide Bandgap

Semiconductors (WBG):

GaN/AlGaN

Semiconductor nanodevices in ROOTHz

Final objective: fabrication of THz detectors and emitters with the same technology



ROOTHz Project



Outline

Outline


1 µm

V (V)

-3 -2 -1 0 1 2 3

Curr

ent

( A

)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

W approx. 60 nm

W approx. 70 nm

+

+ + + + +

+ + + + +

V>0, channel open

– – – – –

–

– – – – –

InP InP

InP - substrate

InGaAs

d doping

InGaAs channel

nanochannel

Self-Switching Diodes (SSDs)

V<0, channel closed


Adequate geometry for the onset of Gunn

oscillations

Tuneable threshold voltage from almost zero to more than

ten volts by adjusting the channel width

Simple technological process: etching of insulating trenches on a semiconductor

surface

Easy downscaling and parallelization: THz operation can be

obtained




• THz Detection: non-linear I-V characteristics

Use of NBG materials (Room Temperature ballistic transport) for increased

sensitivity and broadband

• THz Emission: Gunn Effect in InGaAs, and GaN !!

Use of WBG materials for increased power and frequency

• Planar geometry (and antennas) allow for a better coupling

• Parallelization for enhanced performances (and correct thermal management)



ROOTHz Project


Conclusions / Persp.

Outline

Outline

SSDs as THz detectors

SSDs as THz emitters


SSDs as THz detectors: experiments

3 m

2DEG

V

1 mm

C. Balocco et al., Appl. Phys. Lett. 98, 223501 (2011)

Room temperature

THz detection

4 diodes in

parallel -1.0 -0.5 0.0 0.5 1.0-4

0

4

8

12

16

20

Cu

rren

t (

A)

Voltage (V)

B

0.0 0.2 0.4 0.6 0.8-35

-30

-25

-20

-15

-10

-5

0

Outp

ut

DC

Voltage (

mV

)

Bias Current (A)

150 mV/mW

300 mV/mW T = 300 K

Responsivity

1330 V/W @ 12 K

Free Electron

Laser at 1.5 THz


3 m

2DEG

V

THz imaging using black body radiation


4 diodes in parallel


600nm

Interdigital InGaAs mesa with 2000 etched SSDs


• Corner frequency below 100 kHz even at relatively high biases

• NEP @ 110 GHz ~ 65 pW/Hz1/2 comparable to SBD

Noise can be reduced by increasing the number of SSDs in parallel

100m 1 10 100 1k 10k10

0

101

102

103

104

105

106

Vo

ltag

e n

ois

e (

nV

/Hz1

/2)

Frequency (Hz)

200 nA

300 nA

500 nA

1 A

2 A

no bias

1/f noise


SSDs as THz detectors: Monte Carlo simulations

LC=250 nm

WC=50 nm

WV=20 nm

WH=5 nm

175 nm 175 nm

In0.53Ga0.47As

T=300 K

• THz Detection: non-linear I-V characteristics Use of NBG materials (Room Temperature ballistic transport) for increased

sensitivity and broadband. Possibility for RESONANT DETECTION

AC to DC

rectification

Frequency (THz)

0.1 1

Re

ctifi

ed

DC

cu

rre

nt (A

/m)

0.0

0.5

1.0

1.5

2.0

Vo=0.25 V

V=Vosen(2pf)

I

1.4 THz

Enhanced rectification in the THz range

(tunable by geometry)


THz dynamics in SSDs: pump-probe experiments

fs laser excitation beam 400 nm

Bias

Sampling beam 800 nm

Schematics of electro-optic (EO) sampling

EO crystal

Experiments done at Univ. of Rochester by Jie Zhang and Roman Sobolewski


Time (ps)

15 17 19 21 23

Curr

ent (A

/m)

-1000

0

1000

2000

3000

Exp

eri

me

nta

l (a

. u.)

-6

-4

-2

0

2

4

6

8

Experimental

V=1.0 V

V=-1.0 V

V=0.0 V

SSDs as THz detectors: pump-probe experiments

MC simulations predict a much sharper peak (1/3 FWHM), but the shape is similar

THz oscillations may be emitted from the excitation of the SSDs with fs-lasers


29 nm

38 nm

SSDs as THz detectors: InAs technology

Progress in InAs SSDs technological process

higher mobility improved responsivity and fc

650 nm



ROOTHz Project


Conclusions / Persp.

Outline

Outline

SSDs as THz detectors

SSDs as THz emitters


SSDs as THz emitters: Gunn oscillations

• Suitable geometry: vertical trench focuses

the electric field at the cathode side of the

channel, and anode voltage increases electron

concentration onset of domains and

propagation along the channel

Cointegration with detectors

• Material: GaN channels

High saturation velocity, low energy

relaxation time high frequency

High threshold field high power

Planar design SSDs in parallel

facilitates heat dissipation

(a)

(b)

n+ n- n n+


SSDs as THz emitters: Monte Carlo simulations

V (V)

25 30 35 40 45 50 55 60 65

Fre

quency

(G

Hz)

300

350

400

450 (b)

LC=900 nm

WC=75 nm

WV=100 nm

WH=50 nm

500 nm 150 nm

GaN T=300

K

Time (ps)

10 15 20 25 30 35 40 45 50

I (m

A)

0.4

0.8

1.2

1.6

2.0(a)

30 V

40 V

50 V

60 V

V (V)

-40 -20 0 20 40 60

I (m

A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Gunn

Oscillations

in GaN

SSDs

Monte Carlo Simulations

Oscillation frequencies above 400 GHz (voltage controlled and tunable by geometry)


Unexpectedly high surface charge too low electron concentration in the channel no Gunn oscillation observed (on probe electrical measurements)

Monte Carlo constant surface charge model fails new model (self-consistent model) in order to fit the experimental results

Experimental results: Run 1 of GaN SSDs

16 parallel GaN SSDs


Bias (V)

-10 -5 0 5 10 15 20

Curr

ent (m

A)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Experimental

MC

L= 500 nmW=500 nm

Bias (V)

-10 -5 0 5 10 15 20

L= 500 nmW=750 nm

Bias (V)

-10 -5 0 5 10 15 20

Curr

ent (m

A)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5L= 500 nmW

in=350 nm

Wout

=450 nm

(a)

Experimental

MC

(b)

Experimental

MC

(c)

200 nm 450 nm L= 500 nm

50 nm

W=500 nm, 750 nm

100 nm

200 nm 450 nm L=500 nm

Win=350 nm

50 nm

100 nm (a) (b)

Wo

ut=4

50

nm

400 nm

400 nm

New strategies in the design


Wider square SSDs V-Shape SSDs

V-shape GaN SSDs

New Monte Carlo Self-consistent surface charge model GOOD AGREEMENT


Square SSDs: W ≥ 500 nm to provide Gunn oscillations (much wider that initially expected!!) VERY STRONG HEATING

V-shaped SSDs facilitate the onset of oscillations:

o Lower threshold voltage (30V instead of 50V in square SSDs) o Narrower channels are needed (W ≥ 200 nm)

Heating is much reduced with the V-shape

geometry


200 nm 450 nm L= 500 nm

50 nm

W=500 nm, 750 nm

100 nm

200 nm 450 nm L=500 nm

Win=350 nm

50 nm

100 nm (a) (b)

Wo

ut=4

50

nm

400 nm

400 nm

New strategies in the design

Wider square SSDs V-Shape SSDs

V-shape GaN SSDs


Free space measurements (devices with antenna mounted on PCB and Si lens)

In spite of large effort in characterization of emission in RF and THz no evidence of

oscillations were found in Run 2

Pulsed-mode measurements developed



Run 3 fabricated



1.8 mm

Z ~ 120 Ω

720 µm 4 µm

Bow-tie Emission not perpendicular

Z ~ 75 Ω

Equiangular spiral Emission perpendicular

Integration with adequately designed

broadband antennas



Good control of the technology



Structures designed for optimized heating

Higher bias can be applied (above the

threshold for the onset of oscillations)

No emission observed yet

Free-space characterization

Guided-wave characterization

under probes



Desynchronization of the oscillations: MC simulations

Single SSD

4-SSDs

2-SSDs

More SSDs in parallel, more pronounced desynchronization

An external resonator is needed for synchronization


Resonant circuit modeling

• Series and parallel RLC circuits already implemented

• Circuit equations (solved in the time domain) coupled to the MC current

The voltage between terminals is fixed by the RLC circuit


Resonant circuit modeling

f0 (GHz)

100 200 300 400 500 600

Effic

ien

cy (

%)

0.00

0.05

0.10

0.15

0.20

300K

500KConstant quality factor Q=117.8

C (fF) L (nH) R (MW) f0

0.073 33.0 2.5 102.3

0.061 27.5 2.5 122.7

0.050 22.5 2.5 150.1

0.042 19.0 2.5 177.7

0.039 17.5 2.5 192.9

0.031 14.0 2.5 241.1

0.022 10.0 2.5 337.6

0.020 9.0 2.5 375.1

0.017 7.5 2.5 450.2

0.010 4.5 2.5 750.3

Resonant frequency f0=1/(2pLC)

Crosstalk capacitance of about 5 fF can kill

the oscillations

Around 100 SSDs in parallel needed to avoid its effect

Very small capacitances

Heating is not blocking the oscillations

New design iteration with integrated resonant circuit

needed For N parallel diodes C×N, L/N and R/N



ROOTHz Project



Outline

Outline


Future work

THz detection:

• Fabrication, THz characterization and optimization of InAs SSDs as detectors

• Spectral characterization of the responsivity of the SSDs (InGaAs, GaN and InAs) Identification of plasma resonances • GaN SSDs as THz detectors (two patents filed):

- Mixing of THz signals (heterodyne detection)

- Direct demodulation of THz signals (ultra-high bandwidth detection) • Graphene SSDs

THz emission (main focus):

• High frequency (>900 GHz) FTIR cryogenic detection • Design and fabrication of optimized structures with resonant circuits


ROOTHz: Semiconductor Nanodevices for Room

Temperature THz Emission and Detection

www.roothz.eu

J. Mateos

S. Pérez

B. G. Vasallo

I. Íñiguez-de la-Torre

J. Millithaler

A. Íñiguez-de la-Torre

S. García

A. M. Song

A. Rezazadeh

M. Hallsall

C. Balocco

L. Zhang

Y. Alimi

C. Gaquiere

G. Ducournau

P. Sangaré

J. Grahn

P. A. Nilsson

H. Rodilla

A. Westlund

H. Zhao

Acknowledgements

Institut d’Électronique du Sud Université Montpellier II

J. Torres L. Varani P. Nouvel A. Penot

Jie Zhang Roman Sobolewski


Thanks for the attention !

university of salamanca, spain - fapesp of salamanca, spain ... thz radiation can be used to...

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