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Register a new userRoom Temperature Coherent and Voltage Tunable Terahertz Emission from Nanometer-Sized Field Effect Transistors
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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 channels current are observed and explained as due to the increase of the carriers density and drift velocity.
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The unique optoelectronic properties of graphene [1] make it an ideal platform for a variety of photonic applications [2], including fast photodetectors [3], transparent electrodes [4], optical modulators [5], and ultra-fast lasers [6]. Owing to its high carrier mobility, gapless spectrum, and frequency-independent absorption coefficient, it has been recognized as a very promising element for the development of detectors and modulators operating in the Terahertz (THz) region of the electromagnetic spectrum (wavelengths in the hundreds of micrometers range), which is still severely lacking in terms of solid-state devices. Here we demonstrate efficient THz detectors based on antenna-coupled graphene field-effect transistors (FETs). These exploit the non-linear FET response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature (RT) operation at 0.3 THz, with noise equivalent power (NEP) levels < 30 nW/Hz^(1/2), showing that our devices are well beyond a proof-of-concept phase and can already be used in a realistic setting, enabling large area, fast imaging of macroscopic samples.
Graphene is considered as a promising platform for detectors of high-frequency radiation up to the terahertz (THz) range due to graphene$$s superior electron mobility. Previously it has been shown that graphene field effect transistors (FETs) exhibit room temperature broadband photoresponse to incoming THz radiation thanks to the thermoelectric and/or plasma wave rectification. Both effects exhibit similar functional dependences on the gate voltage and therefore it was found to be difficult to disentangle these contributions in the previous studies. In this letter, we report on combined experimental and theoretical studies of sub-THz response in graphene field-effect transistors analyzed at different temperatures. This temperature-dependent study allowed us to reveal the role of photo-thermoelectric effect, p-n junction rectification, and plasmonic rectification in the sub-THz photoresponse of graphene FETs.
Experimental results of direct measurement of resonant monochromatic terahertz emission optically excited in InGaAs transistor channels are presented. The emission is attributed to two-dimensional plasma waves excited by photogeneration of electron-hole pairs in the channel at the frequency $f_0$ of the beating of two cw-laser sources. The presence of resonances for the radiation emission in the range of $f_0pm 10$ GHz (with $f_0$ 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.
In this study, InSb nanowires have been formed by electrodeposition and integrated into NW-FETs. NWs were formed in porous anodic alumina (PAA) templates, with the PAA pore diameter of approximately 100 nm defining the NW diameter. Following annealing at 125C and 420C respectively, the nanowires exhibited the zinc blende crystalline structure of InSb, as confirmed from x-ray diffraction and high resolution transmission electron microscopy. The annealed nanowires were used to fabricate nanowire field effect transistors (NW-FET) each containing a single NW with 500 nm channel length and gating through a 20nm SiO2 layer on a doped Si wafer. Following annealing of the NW-FETs at 300C for 10 minutes in argon ambient, transistor characteristics were observed with an ION ~ 40 uA (at VDS = 1V in a back-gate configuration), ION/IOFF ~ 16 - 20 in the linear regime of transistor operation and gd ~ 71uS. The field effect electron mobility extracted from the transconductance was ~1200 cm2 V-1 s-1 at room temperature. We report high on-current per nanowire compared with other reported NW-FETs with back-gate geometry and current saturation at low source-drain voltages. The device characteristics are not well described by long-channel MOSFET models, but can qualitatively be understood in terms of velocity saturation effects accounting for enhanced scattering
The terahertz (THz) frequency range (0.1-10 THz) fills the gap between the microwave and optical parts of the electromagnetic spectrum. Recent progress in the generation and detection of the THz radiation has made it a powerful tool for fundamental research and resulted in a number of applications. However, some important components necessary to effectively manipulate THz radiation are still missing. In particular, active polarization and phase control over a broad THz band would have major applications in science and technology. It would, e.g., enable high-speed modulation for wireless communications and real-time chiral structure spectroscopy of proteins and DNA. In physics, this technology can be also used to precisely measure very weak Faraday and Kerr effects, as required, for instance, to probe the electrodynamics of topological insulators. Phase control of THz radiation has been demonstrated using various approaches. They depend either on the physical dimensions of the phase plate (and hence provide a fixed phase shift) or on a mechanically controlled time delay between optical pulses (and hence prevent fast modulation). Here, we present data that demonstrate the room temperature giant Faraday effect in HgTe can be electrically tuned over a wide frequency range (0.1-1 THz). The principle of operation is based on the field effect in a thin HgTe semimetal film. These findings together with the low scattering rate in HgTe open a new approach for high-speed amplitude and phase modulation in the THz frequency range.
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