1,003 research outputs found
Intersubband magnetophonon resonances in quantum cascade structures
We report on our magnetotransport measurements of GaAs/GaAlAs quantum cascade
structures in a magnetic field of up to 62 T. We observe novel quantum
oscillations in tunneling current that are periodic in reciprocal magnetic
field. We explain these oscillations as intersubband magnetophonon resonance
due to electron relaxation by emission of either single optical or acoustic
phonons. Our work also provides a non-optical in situ measurement of
intersubband separations in quantum cascade structures.Comment: 5 pages, 4 figure
Electrically injected cavity polaritons
We have realised a semiconductor quantum structure that produces
electroluminescence while operating in the light-matter strong coupling regime.
The mid-infrared light emitting device is composed of a quantum cascade
structure embedded in a planar microcavity, based on the GaAs/AlGaAs material
system. At zero bias, the structure is characterised using reflectivity
measurements which show, up to room temperature, a wide polariton anticrossing
between an intersubband transition and the resonant cavity photon mode. Under
electrical injection the spectral features of the emitted light change
drastically, as electrons are resonantly injected in a reduced part of the
polariton branches. Our experiment demonstrates that electrons can be
selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure
Gain and Loss in Quantum Cascade Lasers
We report gain calculations for a quantum cascade laser using a fully
self-consistent quantum mechanical approach based on the theory of
nonequilibrium Green functions. Both the absolute value of the gain as well as
the spectral position at threshold are in excellent agreement with experimental
findings for T=77 K. The gain strongly decreases with temperature.Comment: 7 pages, 3 figures directly include
Towards automated design of quantum cascade lasers
We present an advanced technique for the design and optimization of GaAs/AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier–phonon and carrier–carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of lambda~9 µm GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures. © 2005 American Institute of Physic
Radiative quantum efficiency in an InAs/AlSb intersubband transition
The quantum efficiency of an electroluminescent intersubband emitter based on
InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two
series of oscillations periodic in 1/B are observed, corresponding to the
elastic and inelastic scattering of electrons of the upper state of the
radiative transitions. Experimental results are accurately reproduced by a
calculation of the excited state lifetime as a function of the applied magnetic
field. The interpretation of these data gives an exact measure of the relative
weight of the scattering mechanisms and allows the extraction of material
parameters such as the energy dependent electron effective mass and the optical
phonon energy.Comment: 4 pages, 5 figure
- …