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

The Spin Structure of the Nucleon

We present an overview of recent experimental and theoretical advances in our understanding of the spin structure of protons and neutrons.Comment: 84 pages, 29 figure

Sub-THz imaging using non-resonant HEMT detectors

Plasma waves in gated 2-D systems can be used to efficiently detect THz electromagnetic radiation. Solid-state plasma wave-based sensors can be used as detectors in THz imaging systems. An experimental study of the sub-THz response of II-gate strained-Si Schottky-gated MODFETs (Modulation-doped Field-Effect Transistor) was performed. The response of the strained-Si MODFET has been characterized at two frequencies: 150 and 300 GHz: The DC drain-to-source voltage transducing the THz radiation (photovoltaic mode) of 250-nm gate length transistors exhibited a non-resonant response that agrees with theoretical models and physics-based simulations of the electrical response of the transistor. When imposing a weak source-to-drain current of 5 μA, a substantial increase of the photoresponse was found. This increase is translated into an enhancement of the responsivity by one order of magnitude as compared to the photovoltaic mode, while the NEP (Noise Equivalent Power) is reduced in the subthreshold region. Strained-Si MODFETs demonstrated an excellent performance as detectors in THz imaging

Effect of disorder on the density of states of a two-dimensional electron gas under magnetic field

7th International Symposium on Research in High Magnetic Fields, Inst Natl Sci Appl, Toulouse, FRANCE, JUL 20-23, 2003We have calculated the density of states (DOS) of a two-dimensional electron gas in a perpendicular magnetic field, using a multiple scattering method, in the ultraquantum limit. We have considered doped and disordered 2D systems. The results of the scattering method are compared with direct simulations of disordered samples. Using the DOS, we have studied the metal-insulator transition and the magnetic freeze-out including a comparison with experimental results. (C) 2004 Elsevier B.V. All rights reserved

Discrete states of conduction electrons bound to magnetoacceptors in quantum wells

Discrete states of conduction electrons bound to ionized acceptors are observed in intraband magneto-optical experiments on Be-doped GaAs/Ga0.67Al0.33As quantum wells. The electrons are bound to acceptors by a joint effect of the quantum well and an external magnetic field. The observed transition energies are successfully described using states of single magnetoacceptors. The energies show evidence for oscillatory screening of acceptor potentials. Also, two disorder modes of the cyclotron resonance related to acceptor potential fluctuations are observed at higher filling factors