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NONRESONANT TUNNELING IN SHORT-PERIOD SUPERLATTICES WITH OPTICAL
CAVITIES
M.S. Kagan1, I.V. Altukhov1, S.K. Paprotskiy1, A.N. Baranov2, R.
Teissier2, A. A. Usikova3, N.D. Ilinskaya3, A.D. Buravlev3, V.M.
Ustinov3
1V.A. Kotelnikov Institute of Radio Engineering and Electronics,
Russian Ac. Sci., Moscow, Russia; [email protected], Universit
Montpellier 2, CNRS, Montpellier, France3 A.F. Ioffe
Physico-Technical Institute, Russian Ac. Sci., St. Petersburg,
Russia OUTLINE1. Motivation2. Superlattices 3. Measurements4.
Current-voltage characteristics 5. Nonresonant tunneling 6. Effect
of resonant cavity
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Emission power vs frequencyEmission power vs frequencyEmission
power vs frequency
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SuperlatticesL. Esaki and R. Tsu, IBM J. Res. Devel. 14, 61
(1970). Note, that all semiconductor THz lasers operate at
cryogenic temperatures and can not work at room temperature (kT=25
meV) because the energies of quanta in THz range are around 10 meV
and to obtain the population inversion is practically impossible.
So, we need to reject the laser scheme and to look for another way
to get THz generation at room T. The reasonable idea seems to look
for a semiconductor system with a fast negative differential
conductivity (NDC), which can produce THz oscillations in a
suitable resonant cavity.
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Superlattices InAs/AlSb superlattices:Cap layer: n+-InAs (n =
1x1019 cm-3) - 1 m, 60 periods of 4.5nm InAs/3.5nm AlSb InAs(Si)
QWs: n = (0.5 - 2) 1017 -3 Substrate: n+-InAs, n = 1x1019 cm-3
GaAs/AlAs superlattices:100 periods of 4nmGaAs/2nmAlAs Energy
spectrum and wave functions.40 kV/cm. T = 300 KResonant cavity with
the current leadCavities: ring-shaped gold contacts formed THz
optical cavities for free space l ~ 110 to 160mm. Whispering
gallery mode
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Current-voltage characteristics of InAs/AlSb SLs without cavity.
T = 77 K. Rectangular pulse, matched load resistance.
At low voltages, the current saturation or negative differential
conductivity (NDC) were observed caused by Esaki-Tsu mechanism of
miniband transport at overlapping broadened confined states in
periodic QWs.
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Time dependences of voltage and currentInAs/AlSb superlattices.
=300 , matched load resistance. Current oscillations are due to NDC
of the sample exciting parasitic resonant circuits.
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InAs/AlSb SLs with optical cavities Time dependences of current
and voltage. I-V characteristics in two polarities. = 300 .
Triangular pulse, small load resistance. The current saturation on
initial part of I-V curve is connected with static domain formation
resulted from NDC.
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Current-voltage characteristics of InAs/AlSb SL. T = 300 K.
Triangular pulses, small load resistance (1 Ohm). Inset: scheme of
nonresonant tunnelingNonresonant tunneling and the influence of
optical cavity (Purcell effect)Purcell factor lc/n is the
wavelength within the material, Q is the quality factor, V is the
mode volume of the cavity.
(E.M. Purcell, Phys. Rev. 69, 681, 1946.)
The Purcells paper, where he first entered this factor is one of
the shortest (one paragraph) and at the same time one of the most
cited in the modern physics. E.g., in 2011 there were 1681 citings.
Using for estimation Q=100 we get in our case Fp ~ 1000.
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Measurements.GaAs/AlAsTime dependences of current and voltage.
I-V curves. = 300 . Triangular pulse, small load resistance.
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Measurements.GaAs/AlAsTime dependences of current and voltage.
I-V curves. = 300 .
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Current-voltage characteristics of GaAs/AlAs SL. T = 300 K.
Triangular pulses, small load resistance (1 Ohm).GaAs/AlAs
superlattices with optical cavities100 periods of 4nmGaAs
(QW)/2nmAlAs on heavily doped GaAs substrate.
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ConclusionVertical transport in short-period InAs/AlSb and
GaAs/AlAs superlattices (SLs) was studied. The periodic maxima
observed in the current-voltage characteristics of these SLs in the
nonresonant tunneling regime were attributed to the influence of
optical cavity on optical transitions within quantum wells (Purcell
effect). Certainly, the additional confirmation is desirable for
this explanation, both theoretical and experimental. In particular,
it is necessary to calculate the probabilities of phonon-assisted
and radiative transitions between the confined states in the
neighboring QWs. It would be useful, as well, to study the
current-voltage characteristics of resonant-cavity samples with
different frequencies.
It has been suggested to use the SLs as an amplification medium
for coherent THz electromagnetic field due to Bloch oscillations.
This principle is well known, while its practical realization has
been problematic for a long time because of NDC arisen in SLs,
which is necessary for Bloch wave amplification. The existence of
NDC causes a parasitic formation of the Gunn domains inside the
superlattice, which destroys the mechanism of Bloch gain.