We show theoretically that in quantum wells subjected to a strong magnetic field the intersubband current peaks at magnetic field values, which reveal the underlying specific intersubband scattering ...mechanism. We have designed and grown a superlattice structure in which such current oscillations are clearly visible, and in which the transition from the purely single-electron to the mixed single- and two-electron scattering regimes can be observed by tuning the applied voltage bias. The measurements were conducted in ultrahigh magnetic fields (up to 45 T) to obtain the full spectrum of the current oscillations.
Photocurrent (PC) spectroscopy is employed to study the carrier escape from self-assembled InAs/GaAs quantum dots (QDs) embedded in a Schottky photodiode structure. As a function of the applied ...field, we detect a shift of the exciton ground-state transition due to the quantum-confined Stark effect (
S
=
4.3
meV
/
V
). The tunneling time, which is directly related to the observed photocurrent linewidth due to
τ
∼
ℏ
/
(
2
Γ
)
, changes by a factor of five in the photocurrent regime. The measured linewidth dependency on the electric field is modeled by a simple 1D WKB approximation for the tunneling process, which shows that the energetic position of the wetting layer is important for the measured tunneling time out of the dot. In addition to that we present cross-sectional atomic force measurements (AFM) of the investigated photodiode structure. The method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.
The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within ...this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10(-3) times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10(-5) RIU.
In this review, we report on the study of terahertz (THz) intersubband (ISB) transitions and on the optical devices based on them. We use time-resolved THz spectroscopy to examine ISB optical ...transitions in semiconductor quantum wells and quantum cascade lasers (QCLs). From these measurements, we obtain important information on the carrier relaxation, scattering mechanisms, and the gain. The waveguide losses are studied directly on the QCL devices and we show the main loss mechanism in the double-metal waveguides. Finally, we demonstrate THz-QCLs with low-mode volume optical cavity.
We demonstrate terahertz quantum cascade lasers realized in defect-free ring resonators that are mounted episide-down on a silicon substrate by a die-bonding technique. Devices show much reduced ...threshold current densities and free-running comb formation.
Intraband photocurrent and absorption measurements were performed on InAs/InGaAlAs/InP quantum dot structures. A full three-dimensional theoretical model has been employed to identify the observed ...photocurrent as a bound to bound transition, where the final state is about 200 meV deep below the conduction band continuum. The reported results strongly suggest that an Auger process plays a fundamental role in generating the observed intraband photocurrent.
We present terahertz quantum-cascade lasers based on sub-wavelength circular-shaped double-metal microcavities whose single-mode emission can be fine-tuned via dynamical frequency pulling. This ...allows to estimate the peak gain of the material to
27
cm
-
1
and the shift of the cavity mode towards the gain maximum by 30
GHz. Strong mode confinement in the growth and in-plane directions are provided by a double-plasmon waveguide and due to the strong impedance mismatch between the gain material and air. These ultra-compact devices exhibit threshold currents as low as 13.5
mA. We lifted the natural two-fold degeneracy of the whispering-gallery modes by lifting the rotational symmetry of such resonators.
Terahertz Amplifier with Optical Threshold Kainz, M.A; Jaidl, M.; Limbacher, B. ...
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC),
2021-June-21
Conference Proceeding
Amplifiers of Terahertz (THz) radiation are quite useful, because in this spectral range radiation is normally weak and sensitive detectors are hard to get. Monolithically integrated ...master-oscillator power-amplifier (MOPA) 1 , 2 as well as free-space amplifiers 3 have been demonstrated by using Quantum Cascade laser (QCL) structures with amplifications in the range of 3 - 12 dB. Although these devices are very promising, they all provide a linear amplification. However, for most telecommunication applications an amplification only above a certain threshold is advantageous, since this avoids the amplification of noise.
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