Non-resonant Detection Research Articles

Design and Characterization of Plasmonic Terahertz Wave Detectors Based on Silicon Field-Effect Transistors

We report the first implementation of a modeling and simulation environment for the plasmonic terahertz (THz) detector based on the silicon (Si) field-effect transistor (FET) with a technology computer-aided-design (TCAD) platform. The nonresonant plasmonic behavior has been modeled by introducing a quasi-plasma electron box as a two-dimensional electron gas (2DEG) in the channel region. The alternate-current (AC) signal as an incoming THz wave radiation successfully induced a direct-current (DC) drain-to-source voltage as a detection signal in the broadband sub-THz frequency regime. The simulated dependences of photoinduced DC detection signals on structural parameters such as gate length and dielectric thickness confirmed the operation principle of the nonresonant plasmonic THz detector in the Si FET structure. We evaluated the design specifications of THz detectors considering both responsivity and noise equivalent power (NEP) as the typical performance metrics. The proposed methodologies provide the physical design platform for developing novel plasmonic THz detectors operating in the nonresonant detection mode.

An improved model for non-resonant terahertz detection in field-effect transistors

Transistors operating well above the frequencies at which they have gain can still rectify terahertz currents and voltages, and have attracted interest as room-temperature terahertz detectors. We show that such rectifying field-effect transistors may still be treated as a lumped element device in the limit where plasma resonances of the electron gas do not occur. We derive analytic formulas for important transistor parameters, such as effective rectification length and device impedance using a transmission-line model. We draw conclusions for plasma-resonant detection where possible. We derive the THz response of a field-effect transistor with a two-dimensional electron-gas channel by a Taylor expansion of the drain–source bias. We connect circuit theory to the existing theories that describe the bias in the gated region by differential equations. Parasitic effects, such as the access resistance, are included. With the approach presented in this paper, we derive the responsivity for a novel field detector that mixes a (THz) signal applied between gate and source with another signal applied between drain and source in homodyne or heterodyne operation mode. We further derive expressions for the expected noise-equivalent power (NEP) in direct detection and mixing mode, including parasitic effects, and find that sub-pW/Hz should be achievable for realistic device and material parameters for direct detection and less than 900 K noise temperature for mixing at 10 μW local oscillator power.

Single molecule detection from a large-scale SERS-active Au79Ag21 substrate

Detecting and identifying single molecules are the ultimate goal of analytic sensitivity. Single molecule detection by surface-enhanced Raman scattering (SM-SERS) depends predominantly on SERS-active metal substrates that are usually colloidal silver fractal clusters. However, the high chemical reactivity of silver and the low reproducibility of its complicated synthesis with fractal clusters have been serious obstacles to practical applications of SERS, particularly for probing single biomolecules in extensive physiological environments. Here we report a large-scale, free standing and chemically stable SERS substrate for both resonant and nonresonant single molecule detection. Our robust substrate is made from wrinkled nanoporous Au79Ag21 films that contain a high number of electromagnetic “hot spots” with a local SERS enhancement larger than 109. This biocompatible gold-based SERS substrate with superior reproducibility, excellent chemical stability and facile synthesis promises to be an ideal candidate for a wide range of applications in life science and environment protection.

Terahertz responsivity of field effect transistors versus their static channel conductivity and loading effects

We study the broadband photovoltaic response of field effect transistors on terahertz radiation. A simple physical analytical model of the response is developed. It is based on plasma density perturbation in the transistor channel by the incoming terahertz radiation. The model shows how the non-resonant detection signal is related to static (dc) transistor characteristics. We analyze loading effects related to capacitive, inductive, and resistive coupling of the detector to the read-out circuit as a function of modulation frequencies and loading resistors. As we show, the proposed physical model completed by loading effects fully describes the experimental results on the non-resonant sub-terahertz detection by all studied III-V (GaAs, GaN) and silicon based transistors. Field effect transistors were recently proposed as the best terahertz detecting pixels for fabrication of low cost focal plane arrays for terahertz imaging. This article gives prospects for electrical simulation of these transistors and their optimal integration in the focal plane arrays.

Device loading effect on nonresonant detection of terahertz radiation in dual grating gate plasmon‐resonant structure using InGaP/InGaAs/GaAs material systems

AbstractWe report on nonresonant detection of terahertz radiation using our original InGaP/InGaAs/GaAs plasmon‐resonant high‐electron‐mobility transistor having a dual grating gate (DGG) structure. The experiments were performed at room temperature using a Gunn diode operating at 0.30 THz as the THz source. Using a device‐loading model, the intrinsic responsivity was extracted and was dependent on the polarization of the incident THz wave. The device exhibited highest response when the electric‐field vector of the incident THz radiation was directed in the source‐drain direction. The 2D spatial distribution image of the transistor responsivity shows a clear beam focus centred on the transistor position, which proves the appropriate coupling of the THz radiation to the device, due to the DGG structure. The device also showed a high intrinsic responsivity of ∼90 V/W and a noise equivalent power (NEP) as low as ∼10‐10 WHz‐0.5. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photodissociation of pyrrole–ammonia clusters by velocity map imaging: mechanism for the H-atom transfer reaction

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(n-1) products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (∼0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment.

Room temperature detection of sub-terahertz radiation in double-grating-gate transistors

Room temperature photovoltaic non-resonant detection by large area double-grating-gate InGaP/InGaAs/GaAs heterostructures was investigated in sub-THz range (0.24 THz). Semi-quantitative estimation of the characteristic detection length combined with self-consistent calculations of the electric fields excited in the structure by incoming terahertz radiation allowed us to interpret quantitatively the results and conclude that this detection takes place mainly in the regions of strong oscillating electric field excited in depleted portions of the channel.

Enhanced Plasma Wave Detection of Terahertz Radiation Using Multiple High Electron-Mobility Transistors Connected in Series

We report on enhanced room-temperature detection of terahertz radiation by several connected field-effect transistors. For this enhanced nonresonant detection, we have designed, fabricated, and tested plasmonic structures consisting of multiple InGaAs/GaAs pseudomorphic high electron-mobility transistors connected in series. Results show a 1.63-THz response that is directly proportional to the number of detecting transistors biased by a direct drain current at the same gate-to-source bias voltages. The responsivity in the saturation regime was found to be 170 V/W with the noise equivalent power in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> W/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> . The experimental data are in agreement with the detection mechanism based on the rectification of overdamped plasma waves excited by terahertz radiation in the transistor channel.

Optical–radio-frequency resonances free from power broadening

We have demonstrated a new mode of operation of an optical-radio-frequency double-resonance measurement, which allows high-resolution rf spectroscopy with negligible power broadening. The method is based on saturating, resonant excitation, and nonresonant detection of an atomic alignment of alkali-metal atoms by magneto-optical means. Its application to precision measurements, in particular to atomic magnetometry, is discussed.

Coherent terahertz detection with a large-area photoconductive antenna

We present a nonresonant photoconductive terahertz detection antenna suitable for detection of both focused and unfocused terahertz radiations. Our system consists of a scalable terahertz emitter based on an interdigitated electrode structure and a detection antenna with similar electrode geometry. While the emitter is fabricated on semi-insulating GaAs we compare different ion-implanted GaAs-based detection antennas. We studied the dependence of the measured terahertz signal on the power and spot size of the gating laser pulse. In addition we compare the performance of our antenna with that of electro-optical sampling.

Device loading effects on nonresonant detection of terahertz radiation by silicon MOSFETs

Results of room temperature measurement of nonresonant sub-terahertz detection by nanoscale silicon MOSFETs under a variety of load conditions are reported. The effect of device loading is incorporated into existing response models to explain diminished response in the sub-threshold region, and calculation of noise equivalent power indicates minima near the threshold voltage.

Vibrational Overtone Spectroscopy of Phenol and Its Deuterated Isotopomers

We have measured the OH- and OD-stretching fundamental and overtone spectra of phenol and its deuterated isotopomers under jet-cooled conditions using nonresonant ionization detection spectroscopy and vapor-phase infrared (IR) and near-infrared (NIR) spectra at room temperature using conventional and photoacoustic spectroscopy. The OH- and OD-stretching bands in the jet-cooled spectra are about 1-10 cm(-1) wide and generally show a few Lorentzian shaped peaks. The bands in the room-temperature spectra have widths of 20-30 cm(-1) and display clear rotational profiles. The band profiles in the jet-cooled spectra arise mostly from nonstatistical intramolecular vibrational redistribution (IVR) with specific coupling to "doorway" states, which are likely to involve CH- and CD-stretching vibrations. The transition dipole moment that determines the rotational structure is found to rotate significantly from the fundamental to the third overtone and is not directed along the OH(D) bond. We use these calculated transition dipole moments to simulate the rotational structure. We determine the rotational temperature in the jet-cooled spectra to be about 0.5 K. Anharmonic oscillator local mode calculations of frequencies and intensities of the OH- and OD-stretching transitions are compared with our measured results. The calculated intensities are in good agreement with the absolute intensities obtained from conventional spectroscopy and with the relative intensities obtained from the room-temperature laser spectroscopy.

SOI micromachined 5-axis motion sensor using resonant electrostatic drive and non-resonant capacitive detection mode

This paper presents a 5-axis motion sensor which can detect 3-axis acceleration and 2-axis angular rate using resonant electrostatic driving and non-resonant capacitive detection mode. This sensor is fabricated by silicon on insulator (SOI) bulk-micromachining, and is vacuum sealed by anodic bonding and activation of the non-evaporated getters (NEG). The sensor chip size is 5.0 × 5.0 × 1.7 mm 3. By applying electrostatic reference vibration of a proof mass along Z-axis at resonant frequency of 3.42 kHz, 3-axis acceleration and 2-axis angular rate can be detected capacitively at non-resonant detection mode. Measured acceleration sensitivities along X-, Y- and Z-axis are 1.9, 1.1 and 4.7 V/G, respectively. Angular rate sensitivities around X- and Y-axis are 6.7 and 12 mV/(° s), respectively.

Terahertz detection by GaN/AlGaN transistors

Detection of subterahertz and terahertz radiation by high electron mobility GaN/AlGaN transistors in the 0.2–2.5 THz frequency range (much higher than the cutoff frequency of the transistors) is reported. Experiments were performed in the temperature range 4–300 K. For the lowest temperatures, a resonant response was observed. The resonances were interpreted as plasma wave excitations in gated two-dimensional electron gas. Non-resonant detection was observed at temperatures above 100 K. Estimates for noise equivalent power show that these transistors can be used as efficient detectors of terahertz radiation at cryogenic and room temperatures.

Terahertz Detection Related to Plasma Excitations in Nanometer Gate Length Field Effect Transistor.

ABSTRACTThe channel of nanometre field effect transistor can act as a resonant cavity for plasma waves. The frequency of these plasma waves is in the Terahertz range and can be tuned by the gate length and the gate bias. During the last few years Terahertz detection and emission related to plasma wave instabilities in nanometre size field effect transistors was demonstrated experimentally. In this work we review the recent results on sub-THz and THz detection by 50-300nm gate length III-V HEMTs and Si MOSFETs. We present experimental results on the resonant and nonresonant (overdamped) plasma wave detection and discuss possible applications of nanometre field effect transistors as new detectors of THz radiations.

5-Axis Motion Sensor using SOI Wafer and the Design Method

This paper presents a 5-axis motion sensor that can detect 3-axis acceleration and 2-axis angular rate capacitively. This sensor is fabricated by SOI bulk-micromachining, and is sealed vacuum by anodic bonding and activation of the non-evaporated getters. By applying Z-axis reference vibration of a proof mass with an electrostatic force at resonant frequency, 5-axis motions can be detected capacitively at non-resonant detection mode. How the resonant frequency of driving direction and detection direction of this sensor changed by size of the weight, beam width, beam thickness and beam length, was clarified. Three samples were made by this design method, and acceleration characteristic and angular rate characteristic were measured, and the effectiveness was shown.

Nonresonant detection of terahertz radiation by silicon-on-insulator MOSFETs

The detection of subterahertz (200 GHz) radiation by silicon-on-insulator MOSFETs with submicron gate lengths in the temperature range from ∼8 to 350 K is reported. The photoresponse measured against gate voltage exhibited a maximum near the threshold voltage with the amplitude decreasing with decreasing temperature. The photoresponse reached the maximum at the gate bias close to the threshold voltage and increased with an increase of the drain-to-source current. This behaviour agrees with the mechanism linking the photoresponse to the excitation of the overdamped plasma waves in the transistor channel. The observed effect could be used for non-destructive, contactless testing of silicon very large integrated circuits in situ.

Plasma wave detection of sub-terahertz and terahertz radiation by silicon field-effect transistors

We report on experiments on photoresponse to sub-THz (120GHz) radiation of Si field-effect transistors (FETs) with nanometer and submicron gate lengths at 300K. The observed photoresponse is in agreement with predictions of the Dyakonov–Shur plasma wave detection theory. This is experimental evidence of the plasma wave detection by silicon FETs. The plasma wave parameters deduced from the experiments allow us to predict the nonresonant and resonant detection in THz range by nanometer size silicon devices—operating at room temperature.

Electron transport and terahertz radiation detection in submicrometer-sized GaAs/AlGaAs field-effect transistors with two-dimensional electron gas

The electronic transport and response in the terahertz range are studied in field-effect GaAs/AlGaAs transistors with a two-dimensional high-mobility electron gas. The special interest expressed in such transistors stems from the possibility of developing terahertz-range radiation detectors and generators on the basis of these devices. Measurements of the value and the magnetic-field dependence of the drain-source resistance are used to estimate the electron density and mobility in the transistor channel. Results of magnetotransport measurements are employed to interpret the nonresonant detection observed in transistors with a gate width from 0.8 to 2.5 µm.

Possibility of single-atom detection on a chip

We investigate the optical detection of single atoms held in a microscopic atom trap close to a surface. Laser light is guided by optical fibers or optical microstructures via the atom to a photodetector. Our results suggest that with present-day technology microcavities can be built around the atom with sufficiently high finesse to permit unambiguous detection of a single atom in the trap with $10\ensuremath{\mu}\mathrm{s}$ of integration. We compare resonant and nonresonant detection schemes and discuss the requirements for detecting an atom without causing it to undergo spontaneous emission.