38 research outputs found
Helicity sensitive terahertz radiation detection by dual-grating-gate high electron mobility transistors
We report on the observation of a radiation helicity sensitive photocurrent
excited by terahertz (THz) radiation in dual-grating-gate (DGG)
InAlAs/InGaAs/InAlAs/InP high electron mobility transistors (HEMT). For a
circular polarization the current measured between source and drain contacts
changes its sign with the inversion of the radiation helicity. For elliptically
polarized radiation the total current is described by superposition of the
Stokes parameters with different weights. Moreover, by variation of gate
voltages applied to individual gratings the photocurrent can be defined either
by the Stokes parameter defining the radiation helicity or those for linear
polarization. We show that artificial non-centrosymmetric microperiodic
structures with a two-dimensional electron system excited by THz radiation
exhibit a dc photocurrent caused by the combined action of a spatially periodic
in-plane potential and spatially modulated light. The results provide a proof
of principle for the application of DGG HEMT for all-electric detection of the
radiation's polarization state.Comment: 7 pages, 4 figure
Terahertz magneto-optical spectroscopy of two-dimensional hole and electron systems
We have used terahertz (THz) magneto-optical spectroscopy to investigate the
cyclotron resonance in high mobility two-dimensional electron and hole systems.
Our experiments reveal long-lived (~20 ps) coherent oscillations in the
measured signal in the presence of a perpendicular magnetic field. The
cyclotron frequency extracted from the oscillations varies linearly with
magnetic field for a two-dimensional electron gas (2DEG), as expected. However,
we find that the complex non-parabolic valence band structure in a
two-dimensional hole gas (2DHG) causes the cyclotron frequency and effective
mass to vary nonlinearly with the magnetic field, as verified by multiband
Landau level calculations. This is the first time that THz magneto-optical
spectroscopy has been used to study 2DHG, and we expect that these results will
motivate further studies of these unique 2D nanosystems.Comment: 11 pages, 7 figure
Room Temperature Coherent and Voltage Tunable Terahertz Emission from Nanometer-Sized Field Effect Transistors
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.Comment: 3 figure
Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications
Resonant frequencies of the two-dimensional plasma in FETs increase with the
reduction of the channel dimensions and can reach the THz range for sub-micron
gate lengths. Nonlinear properties of the electron plasma in the transistor
channel can be used for the detection and mixing of THz frequencies. At
cryogenic temperatures resonant and gate voltage tunable detection related to
plasma waves resonances, is observed. At room temperature, when plasma
oscillations are overdamped, the FET can operate as an efficient broadband THz
detector. We present the main theoretical and experimental results on THz
detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape
Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure
Ultrafast electron thermalization - the process leading to Auger
recombination, carrier multiplication via impact ionization and hot carrier
luminescence - occurs when optically excited electrons in a material undergo
rapid electron-electron scattering to redistribute excess energy and reach
electronic thermal equilibrium. Due to extremely short time and length scales,
the measurement and manipulation of electron thermalization in nanoscale
devices remains challenging even with the most advanced ultrafast laser
techniques. Here, we overcome this challenge by leveraging the atomic thinness
of two-dimensional van der Waals (vdW) materials in order to introduce a highly
tunable electron transfer pathway that directly competes with electron
thermalization. We realize this scheme in a graphene-boron nitride-graphene
(G-BN-G) vdW heterostructure, through which optically excited carriers are
transported from one graphene layer to the other. By applying an interlayer
bias voltage or varying the excitation photon energy, interlayer carrier
transport can be controlled to occur faster or slower than the intralayer
scattering events, thus effectively tuning the electron thermalization pathways
in graphene. Our findings, which demonstrate a novel means to probe and
directly modulate electron energy transport in nanoscale materials, represent
an important step toward designing and implementing novel optoelectronic and
energy-harvesting devices with tailored microscopic properties.Comment: Accepted to Nature Physic
SixGey:H-based micro-bolometers studied in the terahertz frequency range
International audienceSiGe-based bolometers originally designed for infrared operation have been tested as detectors of terahertz radiation. The obtained values of the responsivity and noise equivalent power show that these detectors can compete with conventional room temperature detectors such as pyroelectric detectors and Golay cells having an advantage in their compatibility with the CMOS technology