Plasma waves in Field Effect Transistors for THZ detection and generation

The invention relates to a laser device for emitting waves in a frequency range belonging to the terahertz range, characterized in that it includes the following, in combination: a wave guide (1) extending longitudinally along an axis A-A'; a superconducting coil (4) arranged coaxially to the wave guide (1) and arranged at a first end (112) of the wave guide (1); a p-Ge p-doped germanium crystal (3) arranged inside the coil (4) such that the turns of the superconducting coil (4) at least partially surround said p-Ge crystal (3); a cooling means (7) containing a coolant, the superconducting coil (4) and the p-Ge crystal (3) being arranged in the cooling means (7), and the wave guide (1) partially extending outside the cooling means (7); and a means (13) for removing the coolant from the wave guide

Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3-14%) than the observed optical transition energies.

We report on investigations of photovoltaic response of Si-MOSFETs subjected to terahertz radiation in high magnetic fields. Then a DC drain-to-source voltage is developed that shows singularities in magnetic fields corresponding to paramagnetic resonance conditions. These singularities are investigated as a function of incident frequency, temperature and two-dimensional carrier density. We tentatively attribute these resonances to spin transitions of the electrons bound to Si dopants and discuss the possible physical mechanism of the photovoltaic signal generation

The current flowing in two-dimensional channel of field effect transistors can generate different types of charge density perturbations. They can have a form of uncorrelated hot plasmons or plasma waves. The mechanism of plasma wave generation depends on the parameter omega t and on boundary conditions of the channel. At omega t << 1 only hot plasmons can be generated. The THz emission due to radiative decay of hot plasmons has a broad spectrum and can be only poorly controlled by the transistor gate. The tunability of THz emission can be obtained in the case of the Dyakonov-Shur plasma wave instability. In this work we present experimental studies of THz emission in InGaP/InGaAs/GaAs and GaN/AlGaN based field effect transistors. We report on two types of emission onset: (i) a smooth one typical for hot plasmons generation and (ii) threshold-like one characteristic for plasma waves instabilities. The tunability and spectra of emission change depending on the transistor configuration. We discuss the results suggesting several possible mechanisms of plasma wave excitation.

We report on the resonant detection of a 3.1 THz radiation produced by a quantum cascade laser using a 250 nm gate length GaAs/AlGaAs field effect transistor at liquid nitrogen temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is enhanced by increasing the drain current and driving the transistor into saturation regime. These results clearly show that plasma wave nanometer-size transistors can be used as detectors in all-solid-state terahertz systems where quantum cascade lasers act as sources.

Recent advances in materials and device structures for terahertz imaging and sensing technology are reviewed. The fundamental physical principle for terahertz imaging/sensing is focused on the nonlinear dynamics of plasmons in two-dimensional semiconductors including quantum wells in III-V based heterostructures as well as graphene.