Physical Phenomenafor TeraHertz

Electronic DevicesJérémi TORRES

Institute of Electronics of the SouthUniversity Montpellier

France

Outline

•TeraHertz : Generalities

•Physical phenomena

1. Plasma-waves

2. Optical-phonon resonance

3. Conclusions

The High-Frequency Investigation Group

MicrowavesAntennas/

RadarsEM

CompatibilityRFID

TheoryMonte Carlo

HydrodynamicDrift-Diffusion

ExperimentsPhotoexcitation

THz devicesNear-field

EM cartography

The TeraHertz “gap”

Low costCompact

Room temperature Continuous-wave

TunableIntegration

Electronics Photonicsf = 1012 Hz, 300 GHz - 10 THz, λ = 1 mm - 30 μm

Proc. of IEEE 23, 10 (2005)

Power vs frequency

Optical THz DevicesIndirect

• Laser Beating + photoconductor

• Femtosecond laser + nonlinear cristal

Difficulties: complexity, cost, magnetic field, maintenance,

temperature

Direct• Gas laser• Free electron laser• p-Ge laser• Quantum cascade laser

Electronic THz Devices

Indirect• Multiplication

• Nonlinearities

Difficulties: current, temperature, contact resistance,

efficiency, noise

Direct• Gunn, RTD, Impatt diodes• Schottky, varactor diodes• Magnetron, Carcinotron• FETs, HEMTs

Main Features of THz Radiation

•Non ionizing

•Strong interaction with molecules

•Transmitted through many materials

•Higher resolution than microwaves

Applications in SpectroscopyPhysics: THz Time Domain Spectroscopy,

dynamics of electrons, holes, phonons

Applications in SpectroscopyChemistry: chemical reactions, combustion,

pollution, environment control

(Grischkowski, Oklahoma State Univ.)

Applications in SpectroscopyAstronomy: atmospheric window, detection of molecules, atoms, ionized gas

Progr. Quant. Electr. 28, 1 (2004)

Applications in TelecommunicationsTeraHertz antennas, wireless

communication

http://www.spiegel.de

Applications in Art

Applications in Imaging (T-Ray)

Inspection materials/devices/systems

Industry(Planken, Univ. Delft)

Applications in Imaging (T-Ray)

Medicine

Tooth decay(TeraView)

Applications in Imaging (T-Ray)

Medicine

Dermatology(Teraview)

Courtesy of Teraview

Applications in Imaging (T-Ray)Security

1. THz Nanotransistors

… exploiting plasma waves

Experiments on InGaAs HEMTs

Origin of the peaks?

Appl. Phys. Lett. 80, 3433 (2002)

THz oscillations from plasma-waves

3D plasma oscillations Analogy : harmonic oscillator

Practical applications : High Electron Mobility

Transistor

Tunable frequency with Vg

Travelling plasma waves

vdrift+vplasmavdrift-vplasma

Travelling plasma waves

Mascaret over the Dordogne riverhttp://www.archaero.com/mascaret.htm

Stationary plasma waves

n = 1 f = 0.9 THz n = 3 f = 2.7 THz

Plasma waves in HEMTs

Plasma synchronization by optical beating

Appl. Phys. Lett. 89, 201101 (2006)

THz beating

Detection of THz beating + THz generation

Appl. Phys. Lett. 89, 201101 (2006)

Experiments(detection)

Simulation(generation+detection)

Frequency (GHz)

⟨VDS⟩

δ VDS

Resonant frequency vs swing voltage

3f0

f0

5f0

Provides frequency tuningIEEE J. Sel. Top. Quant. Electron. 14,

491 (2008)

Enhancing detection

Experiments

Simulation

Journ. Appl. Phys. 106, 013717 (2009)

Modeling

THz imaging with HEMT

Non resonant detection

F. Teppe et al., to be published (2009)

Summary of plasma waves nanotransistors

Detector/EmitterRoom temperatureFrequency tuning

Integration

Emission mechanism?

Power?

2. TeraHertz MASER

… or exploiting the optical-phonon transit-time resonance in nitrides

Scattering rates in GaN at T=10 K

J. Appl. Phys. 89, 1161 (2001)

low energies: acoustic and impurity scatteringhigh energies: optical phonon emission

The optical-phonon transit-time resonance

Energy

acceleration τE

optical

phonon

Scat

terin

g ra

teτ -

τ +

τ- : Average relaxation timeτE : Carrier transit time τ+ : Time for optical phonon emission

Advantages of nitrides

Stronger electron-phonon couplingMuch sharper threshold

J. Appl. Phys. 89, 1161 (2001)

InN, T=10 K

InN, T=10 K

InN, T=10 K

InN, T=10 K

Summary of amplification bands

Phys. Rev. B 76, 045333 (2007)

Design of a cavity and emitted power

Gain depends on the electric field

large E

low E

Summary of TeraHertz MASER

SimpleFrequency tuningHigh amplificationNo magnetic field

77 KHigh quality

materialHigh field

Conclusions• Exciting field for theory and experiments

• Junction electronics/optics

• New phenomena, materials, devices, systems

Sujet de stage

« Etude expérimentale des oscillations Gunn et de plasma

téraHertz dans des composants de la micro-électronique »