We report an anomalous wide broadening of the emission spectra of an electronic excitation confined in a two-dimensional potential. We attribute these results to an extremely fast radiative decay rate associated with superradiant emission from the ensemble of confined electrons. Lifetimes extracted from the spectra are below 100 fs and, thus, 6 orders of magnitude faster than for single particle transitions at similar wavelength. Moreover, the spontaneous emission rate increases with the electronic density, as expected for superradiant emission. The data, all taken at 300 K, are in excellent agreement with our theoretical model, which takes into account dipole-dipole Coulomb interaction between electronic excitations. Our experimental results demonstrate that the interaction with infrared light, which is usually considered a weak perturbation, can be a very efficient relaxation mechanism for collective electronic excitations in solids.
We report on reflective electro-optic sampling measurements of TeraHertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. We establish that the physical mechanism of the coherent TeraHertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel's current are observed and explained as due to the increase of the carriers density and drift velocity.T.
We study the incandescence of a semiconductor
system characterized
by a radiatively broadened material excitation. We show that the shape
of the emission spectrum and the peak emissivity value are determined
by the ratio between radiative and nonradiative relaxation rates of
the material mode. Our system is a heavily doped quantum well, exhibiting
a collective bright electronic excitation in the mid-infrared. The
spontaneous emission rate of this collective mode strongly depends
on the emission direction and, uncommonly for an intersubband system,
can dominate nonradiative scattering processes. Consequently the incandescence
spectrum undergoes strong modifications when the detection angle is
varied. Incandescence is modeled solving quantum Langevin equations,
including a microscopic description of the collective excitations,
decaying into electronic and photonic baths. We demonstrate that the
emissivity reaches unity value for a well-defined direction and presents
an angular radiative pattern that is very different from that of an
oscillating dipole.
We report experimental evidence of longitudinal optical (LO) phonon-intersubband polariton scattering processes under resonant injection of light. The scattering process is resonant with both the initial (upper polariton) and final (lower polariton) states and is induced by the interaction of confined electrons with longitudinal optical phonons. The system is optically pumped with a mid-IR laser tuned between 1094 cm -1 and 1134 cm -1 (=9.14 m and =8.82 m). The demonstration is provided for both GaAs/AlGaAs and InGaAs/AlInAs doped quantum well systems whose intersubband plasmon lies at 10 m wavelength. In addition to elucidating the microscopic mechanism of the polariton-phonon scattering, that is found to differ substantially from the standard single particle electron-LO phonon scattering mechanism, this work constitutes the first step towards the hopefully forthcoming demonstration of an intersubband polariton laser.
Experimental results of direct measurement of resonant monochromatic terahertz emission optically excited in InGaAs transistor channels are presented. The emission is attributed to twodimensional plasma waves excited by photogeneration of electron-hole pairs in the channel at the frequency f0 of the beating of two cw-laser sources. The presence of resonances for the radiation emission in the range of f0 ± 10 GHz (with f0 from 0.3 up to 0.5 THz) detected by a Si-bolometer is found. Numerical results support that such a high quality of the emission resonances can be explained by the approach of an instability in the transistor channel.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.