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Intense Terahertz Excitation of Semiconductors
S.D. Ganichev
University of Regensburg
Why Intense Terahertz Excitation of Solids?
ω ~ characteristic energies in solids like: size-quantization energies of QWs, optical phonon energies, plasma oscillation energy, Landau levels, Rashba-Dresselhaus spin splitting of subbands etc.
THz range + high radiation intensity: new phenomena and various nonlinear effects whose characteristic features are basically different from the corresponding effects in the microwave or visible range.
ω < Eg: effects of carrier redistribution in momentum space and on the energy scale.
Molecular physics and biology: THz radiation does not pose an ionization hazard for biological tissue, many biological molecules exhibit vibrational and rotational modes at THz frequencies
~
THz range frequency: between 0.3 THz and 10 THz wavelengths λ: from 1000 µm to 30 µm photon energies ω: from 1 to 35 meV
Intense Terahertz Excitation of Semiconductors
Fills the gap between nonlinear optics/opto-electronics and microwave physics/transport phenomena
New regimes of electron transport, powerful tools for exploring non-linear dynamics in semiconductor nanostructures
Transition from semiclassical physics with a classical field amplitude to the fully quantized limit with photons
Novel methods of material characterization
Concepts of terahertz devices important for development ofterahertz technology
High-Power Terahertz Centers aimed to Semiconductor Physics
Ioffe-Institute/Regensburg Univ.molecular lasers, since 1980
High intensities nanosecond pulses0.15 - 75 THz, single lines
Univ. of California Santa Barbarafree electron laser, since 1988
Moderate intensities microsecond pulses0.15 - 5 THz, tunability
European User Center "FELIX"free electron laser, since 1994
High intensities picosecond pulses1 - 75 THz, tunability
German User Center Rossendorffree electron laser, THz: planned for 2006
High intensities sub-picosecond pulses3 - 60 THz, tunability
Regensburg High-Power Terahertz Center
0 200
t ( n s )
101
102
103
104
CH3F
D2O
NH3
NH3
NH3CO
2
Energy ( meV )
10 100 1000Wavelength ( µm )
Inte
nsity
( k
W/c
m2 )
1
10
Electric field ( kV
/ cm
)
100 10 1
CH3F
CH3F
NH3
Frequency (THz) 30 3 0.3
100Regensburg
Regensburg Terahertz Center
[S.D. Ganichev, et al, JETP Lett., 35, 368 (1982)]
• Intensity: up to 10 MW/cm2 • Pulse duration: ~ 100 ns• Wavelength: 25 µm - 2000 µm
Two high power THz laser systems
two 100 MW mid-infrared lasers, λ = 4.6 µm - 10.8 µm
stable cw-THz laser, λ = 30 µm - 2000 µm, ~100 mW power
60 Watt cw-CO2 laser, λ = 4.6 µm - 10.8 µm
2 kW CO2 Q-switch laser, λ = 4.6 µm - 10.8 µm, 300 ns pulses
THz Q-switch laser, λ = 30 µm - 2000 µm, 300 ns pulses, high stability
Microwave sources: 375 GHz (8mm) and 100 GHz (3.3 mm)
Intense Terahertz Excitationof Semiconductors atRegensburg Center
THz Tunneling Non-linear THz Optics
Hot ElectronsPhotocurrents
THz Device Physics
Spin phenomena
THz Material Physics Biology
THz Tunneling
Phonon assisted tunneling [Phys. Rev. Lett. 71, 3882 (1993)]
Tunneling time [Phys. Rev. Lett. 75, 1590 (1995)]
Drastical enhancement of tunneling in THz range [Phys. Rev. Lett. 80, 2409 (1998)]
Radiation pressure mediated tunneling [JETP. Lett. 44, 301 (1986)]
Spin dependent tunneling [Phys. Rev. B. Rap. Comm. 67, R201304 (2003)]
- Frequency times tunneling time is about unity, ωτ ~ 1- Large number of photons, much more photons per power in the THz-range - Resonance with energy levels in semiconductors- Quasi-optical methods result in a highly senitive detection - High intensities may result in essential ponderomotive action of light
Tunneling in high frequency alternating fields and tunneling in static fields assisted by high
frequency radiation
THz Tunneling
Radiation pressure mediated tunneling
Ref
lect
ion
1
λ = 27 µmp λ (µm)
THz
n-GaAs R
semitransparent metal electrode
10 100 1000
Wavelength (µm)
λp
λ > λp
λ < λp
plasma reflection
n-GaAs
n-GaAs
bΦ
0 x0 x* x
metalTHz Ph
otoc
ondu
ctiv
ity
0
1
2
THz
THz Tunneling
Drastic enhancement of tunneling in THz range
Quasy-static tunneling High-frequency tunneling Multi-photon transitions
ωτ
100
10
10 1 2 3
P(ω
) /
P(ω
=0)
Ge:Hg AlGaAs:Te
E
ε
ωτ < 1Field frequency
ωτ >> 1
n ω
I
ωτ > 1
E ( ω )
ionization of deep impuritiesω << εb
THz frequencies are aboutreciprocal tunneling time
Multi-photon excitation beyond the perturbation limit [JETP. Lett. 37, 901 (1983)]
Spin sensitive bleaching in QWs [Phys. Rev. Lett. 88, 057401 (2002)]
Terahertz absorption saturation [Semiconductors 21, 615 (1987)]
Near-field effects [phys. stat. sol. a 175, 289 (1999)]
Linear-circular dicroism of multi-photon absorption [Phys. Solid State 35, 104 (1993)]
Multi-photon vibronic excitation [Phys. Rev. B Rapid Comm. 52, R8617 (1995)]
- Large number of photons per watt- Transition from semiclassical to fully quantized limit- Resonances with vibrational and rotational modes at- Free electron absorption
Non-linear THz Optics
THz: multi-photon excitation beyond the perturbation limit
Parameter of non-linearity:
η > 1 : regime of fully developed nonlinearity
∝ n-photons n-photons
m-photons
n-photon absorption K ( n ) n - 1 ; ∆ ε = n ω ∝
ε
...
.
...
.
n ω
k
K ( n ) I∝ K ( n - 1 ) ω 3
η =
Multi-photon excitation in the perturbation limit
Absorption oscillates with light intensity (Bessel functions)
Non-linear THz Optics
Circular photogalvanic effect in QWs [Phys. Rev. Lett. 86, 4358 (2001)
Spin-galvanic effect [Nature (London) 417, 153 (2002)]
Magneto-gyrotropic effects [submitted to J. Cond. Matter (2005)]
Spin orientation by current (inverse spin-galvanic effect) [cond-mat (2004)]
Monopolar spin relaxation in QWs [Phys. Rev. Lett. 88, 057401 (2002)]
- Gyrotropic properties of low dimensional electron gas- Angular momentum of circular polarized radiation- Monopolar spin orientation due to small photon energy- Resonances with energy levels in quantum well structures
Spin phenomena
Circular photogalvanic effect
Sy
jx
2DEG
e
ey
σ+
kx0
e2
e1
jx
ε
kx+
Spin phenomena
Circular photogalvanic effect
Sy
jx
2DEG
e
ey
σ+
kx0
e2
e1
jx
ε
kx+
kx0
jx ε
Spin-galvanic effect
Spin phenomena
Circular photogalvanic effect
Sy
jx
2DEG
e
eyBxjx
2DEG
THz radiat ion
σ+
kx0
e2
e1
jx
ε
kx+
kx0
jx ε
Spin-galvanic effect Magneto-gyrotropic effects
ε
k0
j
∆ε = gµBB
.. ... .... ....... ...
. .
.
τε1 τε2<
...... .
...
e1(-1/2)
e1(+1/2)
Spin phenomena
Photon drag effect [JETP. Lett. 35, 368 (1982)]
Linear photogalvanic effect (quantum ratchet) [Appl. Phys. Lett. 77, 3146 (2000)]
Plasma reflection induced photocurrents
in Schottky-diode [JETP Lett. 62, 53 (1995)]
- Effects of carrier redistribution in momentum space and on the energy scale ( ω < Eg)- Ponderomotive action of radiation- Angular momentum of circular polarized radiation- Quantum ratchet effects
Photocurrents
Microwave induced pattern formation [Nature (London) 397, 398 (1999)]
Light impact ionization [JETP Lett. 40, 948 (1984)]
Nonlinear absorption due to light
impact ionization [Appl. Phys. Lett. 64, 1977 (1994)]
Heating and cooling of electron gas in bulk materials [JETP Lett. 38, 448 (1983)]
Heating of 2D electron gas [JETP Lett. 48, 269 (1988)]
THz heating of LO phonons
in δ-doped GaAs [Solid State Communic. 97, 827 (1996)]
- Photon energies can be smaller than optical phonon energy- Effective free electron absorption- Contactless application of high fields- Interplay of phonon emission and photon absorption
Hot Electrons
Light impact ionization ( )
ω = 3meV ω = 224 meV
ωτp >> 1
0 20 40 60 80norm
aliz
ed n
umbe
r of
ge
nera
ted
carr
iers
n-InSbT = 78 K
102
10-1
101
100
10-2
10-3
10-4
E -2 (10-8, V -2*cm2)
∆p = εE(ω)/ω
p0
heating is caused by collisions
E(ω)
Hot Electrons
λ = 385 µm
λ = 152 µm
λ = 90 µm
Spin photocurrents (spin-orbit coupling in band structure, spin relaxation)
[Phys. Rev. Lett. 92, 256601 (2004)]
Saturation spectroscopy (spin and energy relaxtion)
bulk materials: [Semiconductors 16, 179 (1982)]
quantum wells: [J. Appl. Phys. 96, 420 (2004)]
Terahertz phonon assisted tunneling (impurities characterization)
[Phys. Rev. B Rap. Comm. 63, R201204 (2001)]
[Phys. Rev. B 61, 10361 (2000)]
[J. Appl. Phys. 87, 3843 (2000)]
[Phys. Rev. B Rap. Comm. 55, R9243 (1997)]
Light impact ionization (impurities parameters)
[JETP 63, 256 (1986)]
THz µ-photoconductive spectroscopy (relaxation)
[JETP 70, 1138 (1990)]
THz Material Physics
THz laser technique for semiconductor physics [JETP Lett. 35, 368 (1982)]
Photon drag detectors for THz radiation [Tech. Phys. Lett. 11, 20 (1985)]
µ-photoconductive detectors [Tech. Phys. Lett. 11, 377 (1985)]
Polarization detector [Tech. Phys. Lett. 14, 580 (1988)]
Plasma-reflection tunnel diodes [Tech. Phys. Lett. 15, 290 (1989)]
Generation of ps-THz laser pulses [Int. J. Infrared & Milimeter Waves 11, 851 (1990)]
Detector of radiation helicity [Int. J. Infrared & Millimeter Waves 24, 847 (2003)]
Spectral range 2 µm - 2000 µm (75 - 0.15 THz)
THz Device Physics
Tunneling processes induced by terahertz fields,
[J. Biological Physics, 29, 327 (2003)]
Dental tissue analysis and treatment
by interaction with terahertz radiation,
[Int. J. Infrared & Millimeter Waves 21, 407 (2000)]
- THz radiation does not pose an ionization hazard
for biological tissue
- Biological molecules exhibit vibrational and
rotational modes at THz (characteristic fingerprints)
- T-rays can easily penetrate and image inside
most dielectric materials
- Tunneling in proteins induced by contactless
applied THz radiation
Biology
Dental tissue analysis and treatment by interaction with terahertz radiation
0.0
0.5
1.0IIR
= 21 MW/cm2
1090107010501030
Frequency ν ( cm-1 )
ν3
(c)ν
3
(b) ν3
(a)
Ligh
t Int
ensi
ty (
arb
. uni
ts )
1075 1080 1085 10900
5
10
15
20
ν3
(a)
Frequency ν ( cm-1
)Pla
sma
Thr
esho
ld (
MW
/cm
2 )
Detection
Resonance with the spectral position of the PO4 stretch mode
Resonance laser ablation
Biology
RussiaA.F. Ioffe Institute, St. Petersburg
Polytechnical University, St. Petersburg Institute of Radioelectronic, MoscowInstitute of Semiconductor Physics, Novosibirsk
GermanyUniversität Regensburg
Walter Schottky Institute Universität HannoverUniversität GießenTU MünchenUniversität DortmundUniversität WürzburgTU BraunschweigUniversität Bayreuth
USAUniversity of California, BerkeleyNaval Research Lab., WashingtonUniversity of New York, BuffaloUniversity of New York, RochesterUniversity of PurdueM.I.T.
UKUniversity of Surrey, GuildfordHeriot-Watt University, Edinburgh
The NetherlandsEU THz-center "FELIX"
ÖsterreichUniversität LinzUniversität Wien
Japan Tohoku University
FranceUniversity of Toulouse
IsraelTechnion, HaifaBar-Ilanh University
Czech RepublicInstitute of Physics, Prague
UkraineInstitute of Semiconductor Physics, Kiev
IrelandTrinity College, Dublin
Intense Terahertz Excitationof Semiconductors atRegensburg Center
Current projects
- Spingalvanischer Effekt
- Magnetogyrotroper Effekt im Halbleiternanostrukturen
- Monopolare Spinorientierung und Spinrelaxation mit nichtlinearer
Intersubband-Spektroskopie
- Spinphotoströme in Halbleiternanostrukturen
- Terahertz-Nichtlinearitäten in Halbleiter-Nanostrukturen
- Spin dependent tunneling
- Detection of radiation helicity
- Optical and nonlinear properties of nanostructures
Intense Terahertz Excitationof Semiconductors atRegensburg Center
Topics: spin-phenomena, tunneling,
detection principles, light impacz ionization
Tasks for future Intense Terahertz Excitationof Semiconductors atRegensburg Center
(submitted proposals)
- Infrared excited spin photocurrent in SiGe quantum structures
- Spinphotoströme in Quantentrögen und niederdimensionalen
lateralen Halbleiter-Übergittern
- Rein elektrische Spininjektion durch Spin-Bahn-Wechselwirkung in
gyrotropischen Nanostrukturen
- Rashba/Dresselhaus Spinaufspaltung in Quantentrögen
- Dental Tissue Analysis and Treatment by Interaction with Terahertz
Laser Radiation
Topics: spin-phenomena, tunneling,
medicine, characterization of QWs
Tasks for future Intense Terahertz Excitationof Semiconductors atRegensburg Center
(first steps)
- Quantum ratchets
- Zero resistance states at high frequencies
- Helicity dependent currents in carbon nanotubes
- Tunneling controled chirality of molecules
- Light impact ionization prozesses in QWs
- THz tunneling in proteins and molecules
- Fully developed multi-photon transitions in QWs
- Dynamic of spin photocurrents
- Near field spectroscopy of nanostructures
Topics: molecular physics, tunneling, quantum transport
detection principles, near-field effects,
multiphoton processes, light impacz ionization
ratchet effects
Summary Intense Terahertz Excitationof Semiconductors atRegensburg Center
- S.D. Ganichev, and W. Prettl, Intense terahertz excitation of semiconductors Oxford University Press , pp. 1 - 380 scheduled 2005.- S.D. Ganichev, in series ''Advances in Solid State Physics'', B. Kramer (Ed.) (Springer-Verlag Berlin-Heidelberg) Vol. 43, pp. 427-442 (2003).- S.D. Ganichev, and W. Prettl, J. Phys.: Condens. Matter 15, R935 (2003).- S.D. Ganichev, I.N. Yassievich, and W. Prettl, J. Phys.: Condens. Matter 14, R1263 (2002).- S.D. Ganichev, Physica B 273-274, 737 (1999).- S.D. Ganichev et al, in Best of Soviet Semiconductor Physics and Technology (1989-1990), ed. by M. Levinstein and M. Shur (World Scientific, Singapore), 567 (1995).
http://www.physik.uni-regensburg.de/forschung/ganichev/ Reviews:
- novel field in investigations of solids.
- new phenomena and variety of nonlinear effects whose charactersitic features are basically different from the corresponding effects in the microwave range as well as in the range of visible light.
- provide powerful tools for material characterization and for development of THz technology