Field Effect Transistor Detectors Research Articles

A comprehensive Study of the Out of Field Non Target Dose Associated with 6 and 10 MV Flattened and Flattening Filter Free X Ray Beam in a True Beam Linear Accelerator.

To evaluate the out-of-field dose associated with flattened (FF) and flattening filter-free (FFF) 6 and 10 MV X-ray beams in a TrueBeam linear accelerator (Linac). Measurements were taken in a slab phantom using the metal oxide semiconductor field effect transistor (MOSFET) detector at varying depths (dmax, 5 cm, and 10 cm) for clinically relevant field sizes and up to 30 cm from the field edges for 6 and 10 MV FF and FFF beams in TrueBeam Linac. Dose calculation accuracy of the analytic anisotropic algorithm (AAA) and Acuros algorithm was investigated in the out-of-field region. Similarly, the out-of-field dose associated with volumetric modulated arc therapy (VMAT) head-and-neck plan delivered to a body phantom was evaluated. The out-of-field dose for both FF and FFF photon beams (6 and 10 MV) decreased with increasing distance from the field boundary and size. Furthermore, regardless of FF in the field, higher-energy photon beams were associated with lower out-of-field dose. Both algorithms underestimated the dose in the out-of-field region, with AAA failing to calculate the out-of-field dose at 15 cm from the field edge and Acuros failing to calculate out-of-field radiation at 20 cm. At 5 cm from the field edge, an average of 50% underestimation was observed, and at 10 cm, an average of 60% underestimation was observed for both FF and FFF (6 and 10 MV) beams. The VMAT head-and-neck plan performed with the FFF beam resulted in a lower out-of-field dose than the FF beam for a comparable dose distribution. Compared with flattened beams, the FFF modes on TrueBeam Linac exhibited a clinically relevant reduction in the out-of-field dose. Further dosimetric studies are warranted to determine the significant benefit of FFF beams across different cancer sites.

A proposed graphene-gated semiconductor terahertz detector

This paper presents an analytical model for a terahertz wave-controlled graphene-gated semiconductor field-effect transistor (GSFET) operated in the terahertz regime. Analysis has been performed to explore the effect of illumination on the graphene-semiconductor field effect transistor detector in the determination of drain characteristics, transfer characteristics, and transconductance considering both the photoconductive effect and photovoltaic effects. The analysis presented shows the potential of Graphene-HgCdTe FET as a high-speed terahertz detector. From the results, the device is highly sensitive to the exposed terahertz radiation causing a large change in the drain current in comparison to the dark condition which is evident from the drain characteristics.

Contralateral breast radiation doses in breast cancer patients treated with helical tomotherapy.

We aimed to evaluate contralateral breast doses calculated with a Treatment Planning System (TPS) and verified with metal oxide semiconductor field effect transistor (MOSFET) detectors in patients with early-stage breast cancer (BC) who received helical tomotherapy (HT) after breast-conserving surgery. The dosimetric data of 30 patients (15 left-sided and 15 right-sided) with BC treated with 50.4 Gy to the whole breast and 64.4 Gy to the tumor bed in 28 fractions were analyzed. TPS doses were calculated and MOSFET doses were measured in the contralateral breast (CB) at cranial, caudal, and midpoint and 2 cm lateral to the central point. TPS and MOSFET doses were compared in the entire cohort as well as by tumor location (inner vs outer quadrant) and planning target volume of the breast (<1200 cc vs ≥1200 cc). The average doses at superior, inferior, central, and lateral points calculated with the TPS were 0.26 ± 0.15 cGy, 0.21 ± 0.09 cGy, 0.65 ± 0.14 cGy, and 0.50 ± 0.11 cGy, respectively, and were 0.37 ± 0.16 cGy, 0.34 ± 0.12 cGy, 0.60 ± 0.18 cGy, and 0.34 ± 0.15 cGy, respectively in MOSFET readings. Except for the central point, TPS-calculated doses and MOSFET readings were differed. The doses to the CB in patients with inner and outer quadrant tumors were not significantly different. In patients with large breasts, MOSFET doses were higher at superior and lateral points than TPS doses, but TPS doses were greater at inferior points. MOSFET readings were higher than TPS calculated doses in patients with inner or outer quadrant tumors in small or large breast volumes. The dose calculated by the TPS and that measured by MOSFET differed by a very small amount. The maximum dose to the CB administered at the midpoint was 1.8 Gy, as calculated using the TPS and confirmed using MOSFET detectors, in patients with early-stage BC undergoing breast-only radiotherapy with HT.

Development and Evaluation of a Thimble-Like Head Bolus Shield for Hemi-Body Electron Beam Irradiation Technique

Background: The hemi-body electron beam irradiation (HBIe&lt;sup&gt;–&lt;/sup&gt;) technique has been proposed for the treatment of mycosis fungoides. It spares healthy skin using an electron shield. However, shielding electrons is complicated owing to electron scattering effects. In this study, we developed a thimble-like head bolus shield that surrounds the patient’s entire head to prevent irradiation of the head during HBIe&lt;sup&gt;–&lt;/sup&gt;.Materials and Methods: The feasibility of a thimble-like head bolus shield was evaluated using a simplified Geant4 Monte Carlo (MC) simulation. Subsequently, the head bolus was manufactured using a three-dimensional (3D) printed mold and Ecoflex 00-30 silicone. The fabricated head bolus was experimentally validated by measuring the dose to the Rando phantom using a metal-oxide-semiconductor field-effect transistor (MOSFET) detector with clinical configuration of HBIe&lt;sup&gt;–&lt;/sup&gt;.Results and Discussion: The thimble-like head bolus reduced the electron fluence by 2% compared with that without a shield in the MC simulations. In addition, an improvement in fluence degradation outside the head shield was observed. In the experimental validation using the inhouse- developed bolus shield, this head bolus reduced the electron dose to approximately 2.5% of the prescribed dose.Conclusion: A thimble-like head bolus shield for the HBIe&lt;sup&gt;–&lt;/sup&gt; technique was developed and validated in this study. This bolus effectively spares healthy skin without underdosage in the region of the target skin in HBIe&lt;sup&gt;–&lt;/sup&gt;.

To Study the Structural, Optical and Magnetic Properties of Ni-Fe Doped ZnO Diluted Magnetic Semiconductors

The iron and Nickel co-doped in zinc oxide nano-particle, Zn1-x-yFexNiyO {(x=0, y=0), (x=0.05, y=0), (x=0, y=0.05), (x=0.03, y=0.02)} were prepared by Sol-Gel technique. This type of synthesis is used for the manufacture of a Field Effect Transistor (FET) detector which is extremely sensitive, secure, and capable of reproducing. It is also used for the detection of the Piperidine (CH2)5NH (hexahydro pyridone) chemical.&#x0D; The well-closed pack spherical nano-particles of the identified crystalline structure of the usual wurtzite hexagonal phase were achieved by characterization of X-Ray Diffraction (XRD). The blue shift was well observed of Co-doped samples as compared to un-doped or single-doped ZnO nanoparticle samples by UV-visible absorption spectrum. The Fourier Transform Infrared Spectroscopy (FTIR) reveals the existence of chemical bonding and functional groups are established and the occurrence of iron Fe in modes associated with iron Fe in addition to ZnO. The room temperature ferromagnetism was achieved in single or co-doped (Fe-Ni) with ZnO nanoparticles and is confirmed by magnetic characterization (VSM). It was perceived that magnetic saturation was improved in Fe-Ni Co-doped samples relative to pure or single doped. Also, the characterizations of samples show that the exchange interaction of Ni and Fe dominates over Ni-Ni and Fe-Fe interactions.

Dose calculation of 3D printing lead shield covered by biocompatible silicone for electron beam therapy.

This study aims to calculate the dose delivered to the upstream surface of a biocompatible flexible absorber covering lead for electron beam treatment of skin and subcutaneous tumour lesions for head and neck. Silicone (Ecoflex™ 00-30, Smooth-On, Easton, PA, USA) was used to cover the lead to absorb backscattered electrons from lead. A 3D printer (Zortrax M300, Zortrax, Olsztyn, Poland) was used to fabricate the lead shield. Analytic calculation, simplified Monte Carlo (MC) simulation, and detailed MC simulation which includes a modeling of metal-oxide-semiconductor field-effect transistor (MOSFET) detector were performed to determine the electron backscatter factor (EBF) for 6MeV and 9MeV electron beams of a Varian iX Silhouette. MCNP6.2 was used to calculate the EBF and corresponding measurements were carried out by using MOSFET detectors. The EBF was experimentally measured by the ratio of dose at the upstream surface of the silicone to the same point without the presence of the lead shield. The results derived by all four methods agreed within 2.8% for 6MeV and 3.4% for 9MeV beams. In detailed MC simulations, for 6MeV, dose to the surface of 7-mm-thick absorber was 103.7 [Formula: see text] 1.9% compared to dose maximum (Dmax) without lead. For 9MeV, the dose to the surface of the 10-mm-thick absorber was 104.1 [Formula: see text] 2.1% compared to Dmax without lead. The simplified MC simulation was recommended for practical treatment planning due to its acceptable calculation accuracy and efficiency. The simplified MC simulation was completed within 20min using parallel processing with 80 CPUs, while the detailed MC simulation required 40h to be done. In this study, we outline the procedures to use the lead shield covered by silicone in clinical practice from fabrication to dose calculation.

A Compact Current- and Voltage-Mode Model of Antenna-Coupled FET Terahertz Detectors

In this article a comprehensive modeling of cold-biased field-effect transistors (FETs) used as terahertz (THz) detectors is developed. The described model is based upon the transistor Enz-Krummenacher-Vittoz (EKV) model in order to provide valid quantities also near and below the transistor threshold by using available technology parameters, without any extra fitting nor calibration. Important aspects such as the antenna coupling and the effect of amplitude modulation of the THz source are considered in a single, handy, analytical model. THz measurements performed on specifically designed FET detectors confirm its validity, providing a powerful tool and giving a clear insight of the role of available variables. The model can anticipate time-consuming numerical simulations or more physically accurate models requiring experimental parameters calibration, that may complement the results for better accuracy.

Avidin-Biotin Technology in Gold Nanoparticle-Decorated Graphene Field Effect Transistors for Detection of Biotinylated Macromolecules with Ultrahigh Sensitivity and Specificity.

The strong and specific noncovalent interaction between avidin and biotin is widely exploited in different types of enzyme-linked immunosorbent assay kits, labeled immunosensors, and polymer-based sensing devices for the detection of different biomarkers specific to different diseases such as cancer and influenza. Here, we employed the avidin–biotin technology in a novel gold nanoparticle-decorated graphene field-effect transistor (AuNP-GFET) and demonstrated the specific detection of the biotinylated macromolecules such as biotinylated proteins and nucleotides in the sub-picomolar (pM) range. The AuNP-GFET was constructed by fabricating six pairs of interdigital electrodes on graphene transferred on a SiO2/Si substrate. The sensing performance of AuNP-GFET was characterized by the real-time two-terminal electrical current measurement upon injection of the analyte solution into a silicone pool preattached onto the electrodes. Avidin, a tetrameric biotin-binding protein with strong affinity and specificity, immobilized on AuNP-decorated single-layer graphene, was used as the sensing platform and transduced the electrical signal upon binding to the analyte macromolecules. The sensing capability of the AuNP-GFET was tested with the biotinylated protein A. Sensitivity of the present biosensor was estimated to be ∼0.4 pM. The specificity and applicability of the biosensor were confirmed using both synthetic and real samples. Because the biotin label can retain its binding capability to avidin with strong affinity and specificity even after conjugating with varieties of proteins and nucleotides, the present AuNP-GFET biosensor is expected to promote the research in developing different biosensors.

Verification of angular dependence in MOSFET detector

In vivo dosimetry is an essential tool for quality assurance programs, being a procedure commonly performed with thermoluminescent dosimeters (TLDs) or diodes. However, a type of dosimeter that has increasing popularity in recent years is the metal-oxide-semiconductor field effect transistor (MOSFET) detector. MOSFET dosimeters fulfill all the necessary characteristics to realize in vivo dosimetry since it has a small size, good precision and feasibility of meas-urement, as well as easy handling. Nevertheless, its true differential is to allow reading of dose in real time, enabling immediate intervention in the correction of physical parameters deviations and anticipation of small anatomical changes in the patient during treatment. In order for MOSFET dosimeter to be better accepted in clinical routine, information reporting performance should be available frequently. For this reason, this work proposes to verify reproducibility and angular dependence of a standard sensitivity MOSFET dosimeter (TN-502RD-H) for Cs-137 and Co-60 sources. Exper-imental data were satisfactory and MOSFET dosimeter presented a reproducibility of 3.3% and 2.7% (±1 SD) for Cs-137 and Co-60 sources, respectively. In addition, an angular dependence of up to 6.1% and 16.3% for both radioactive sources, respectively. It is conclusive that MOSFET dosimeter TN-502RD-H has satisfactory reproducibility and a considerable angular dependence, mainly for the Co-60 source. This means that although precise measurements, special attention must be taken for applications in certain anatomical regions in a patient.

Analysis of Wide-Bandgap Material OPFET UV Detectors for High Dynamic Range Imaging and Communication Applications

The ultraviolet (UV) photoresponses of Wurtzite GaN, ZnO, and 6H-SiC-based Optical Field Effect Transistor (OPFET) detectors are estimated with an in-depth analysis of the same considering the generalized model and the front-illuminated model for high resolution imaging and UV communication applications. The gate materials considered for the proposed study are gold (Au) and Indium-Tin-Oxide (ITO) for GaN, Au for SiC, and Au and silver dioxide (AgO2) for ZnO. The results indicate significant improvement in the Linear Dynamic Range (LDR) over the previously investigated GaN OPFET (buried-gate, front-illuminated and generalized) models with Au gate. The generalized model has superior dynamic range than the front-illuminated model. In terms of responsivity, all the models including buried-gate OPFET exhibit high and comparable photoresponses. Buried-gate devices on the whole, exhibit faster response than the surface gate models except in the AgO2-ZnO generalized OPFET model wherein the switching time is the lowest. The generalized model enables faster switching than the front-illuminated model. The switching times in all the cases are of the order of nanoseconds to picoseconds. The SiC generalized OPFET model shows the highest 3-dB bandwidths of 11.88 GHz, 36.2 GHz, and 364 GHz, and modest unity-gain cut-off frequencies of 4.62 GHz, 8.71 GHz, and 5.71 GHz at the optical power densities of 0.575 μW/cm2, 0.575 mW/cm2, and 0.575 W/cm2 respectively. These are in overall, the highest detection-cum-amplifi-cation bandwidths among all the investigated devices. The same device exhibits the highest LDR of 73.3 dB. The device performance is superior to most of the other existing detectors along with comparable LDR, thus, emerging as a high performance photodetector for imaging and communication applications. All the detectors show considerably high detectivities owing to the high responsivity values. The results have been analyzed by the photovoltaic and the photoconductive effects, and the series resistance effects and will aid in conducting further research. The results are in line with the experiments and the commercially available software simulations. The devices will greatly contribute towards single photon counting, high resolution imaging, and UV communication applications.

Response Optimization of Antenna-Coupled FET Detectors for 0.85-to-1-THz Imaging

This letter presents several configurations of terahertz (THz) pixel structures with different bow-tie antennas and field-effect transistor (FET)-based detectors, implemented in a 0.15- $\mu \text{m}$ standard CMOS technology, operating at a radiation frequency range of 0.85–1 THz for CMOS imaging applications. The innovative FET detector structures are investigated for higher power coupling efficiency with the integrated antennas, aiming to improve the THz detection behavior in terms of responsivity and noise equivalent power. Experimental THz characterization of the fabricated structures provides the guidelines for the future implementation of THz imaging arrays. Images of concealed metallic objects are acquired in a single-pixel mode under continuous THz illumination.

Evaluating Lens Dose Reduction in Pediatric Neuroradiology Examinations Using Automated Kilovoltage Selection Software.

The purpose of this study is to evaluate the potential of an automated kilo-voltage selection software for the reduction of lens dose in pediatric CT scans. Two metal oxide semiconductor field effect transistor (MOSFET) detectors measured the lens dose in two anthropomorphic 1- and 5-year-old phantoms. These phantoms were scanned using a clinical pediatric brain protocol at 120 kVp as a control with the MDCT scanner. Scans were then repeated using automated kilovoltage software. The automated kilovoltage was set to operate at tube potentials of 120, 110, and 100 kVp. Dose savings were compared with the average lens dose of both eyes between automated kilovoltage and the control setting. Image quality was studied by contrast-to-noise ratios (CNRs) for each setting. The mean (± SD) lens dose from the routine brain scan without automated kilovoltage was 0.92 ± 0.03 cGy and 0.81 ± 0.03 cGy for the 1- and 5-year-old phantoms, respectively. Use of the automated kilovoltage software at 120 kVp, 110 kVp, and 100 kVp resulted in dose reductions of 9.8%, 17.4%, and 19.6%, respectively, for the 1-year-old phantom and 1.2%, 8.6%, and 17.3%, respectively, for the 5-year-old phantom. The CNR for all automated kilovoltage scans was within 11% of the control scans for the 1-year-old and within 6% for the 5-year-old phantom. Our results show that automated kilovoltage software is effective for reducing the radiation dose to the lens of the eye in pediatric patients. Furthermore, the image quality by CNR remained acceptable within 11% of the baseline for all kilovoltage settings used.

Multicolor Spectral-Specific Silicon Nanodetectors based on Molecularly Embedded Nanowires.

Silicon-based photodetectors cannot distinguish between different wavelengths. Therefore, these detectors relay on color-specific filters to achieve color separation. Color filters add complexity to color sensitive device fabrication, and hinder miniaturization of such devices. Here, we report an ultrasmall (as small as ∼20 nm by 300 nm), red-green-blue-violet (RGBV) filter-free spectrally gated field effect transistor (SGFET) detectors. These photodetectors are based on organic-silicon nanowire hybrid FET devices, capable of detecting specific visible wavelength spectrum with full width at half-maxima (fwhm) under 100 nm. Each SGFET is controlled by a distinctive RGBV spectral range, according to its specific organic fluorophore functionalization. The spectral-specific RGBV detection is accomplished via covalent attachment of different fluorophores. The fluorophore molecules inject electrons into the nanowire structure as a result of light absorption at the appropriate RGBV spectral range. These photoinduced electrons modify the occupancies of the oxide's surface states, shifting the device threshold voltage, thus changing its conductivity, and functioning as a negative stress bias in a p-type SiNW FETs. A positive biasing can be achieved via UV light-induced ionization, which leads to detrapping and translocation of electrons at the oxide layer. Furthermore, a novel theoretical model on the mechanism of action of these devices was developed. Also, we show that suspended SGFETs can function as nonvolatile memory elements, which unlike fast-relaxing on-surface SGFETs, can store discrete "on" (RGBV illumination) and "off" (UV illumination) states for several days at ambient conditions. We also demonstrate a unique single-nanowire multicolor photodetector, enabling in principle a broad spectral detection over a single silicon nanowire element. These highly compact, spectral-controlled nanodevices have the potential to serve in various future novel optoelectric applications.

A 400-GHz Graphene FET Detector

This letter presents a graphene field effect transistor (GFET) detector at 400 GHz, with a maximum measured optical responsivity of 74 V/W, and a minimum noise-equivalent power of 130 pW/Hz1/2. This letter shows how the detector performance degrades as a function of the residual carrier concentration in the graphene channel, which is an important material parameter that depends on the quality of the graphene sheet and contaminants introduced during the fabrication process. In this work, the exposure of the graphene channel to liquid processes is minimized resulting in a low residual carrier concentration. This is in part, an important contributing factor to achieve the record high GFET detector performance. Thus, our results show the importance to use graphene with high quality and the importance to minimize contamination during the fabrication process.

CMOS Integrated Lock-in Readout Circuit for FET Terahertz Detectors

In this paper, a switched-capacitor readout circuit topology integrated with a THz antenna and field-effect transistor detector is analyzed, designed, and fabricated in a 0.13-μm standard CMOS technology. The main objective is to perform amplification and filtering of the signal, as well as subtraction of background in case of modulated source, in order to avoid the need for an external lock-in amplifier, in a compact implementation. A maximum responsivity of 139.7 kV/W, and a corresponding minimum NEP of 2.2 nW/√Hz, was obtained with a two-stage readout circuit at 1 kHz modulation frequency. The presented switched-capacitor circuit is suitable for implementation in pixel arrays due to its compact size and power consumption (0.014 mm2 and 36 μW).

Terahertz Heterodyne Communication Using GaAs Field-Effect Transistor Receiver

We report the first successful terahertz heterodyne communication using a field-effect transistor for detection. The communication is a real-time transmission of an uncompressed high-definition TV signal at a data rate of 1.5 Gbps with a 307-GHz carrier frequency. The emitter is a frequency-multiplied amplifier chain whose last stage is a second harmonic mixer that multiplies the carrier signal by the data. The receiver only consists of a GaAs high-electron-mobility transistor that acts as a quadratic receiver, and two 20-dB-gain amplifiers, no limiting amplifier or forward error correction were used. A direct communication would be impossible with such a combination of modulation scheme at emission and quadratic detection at reception, while it is possible in a heterodyne configuration. In addition, for the same source power, the heterodyne scheme allows to increase the communication bandwidth from 80 MHz to more than 2 GHz for a local oscillator power of −8 dBm.

Diffusion part in terahertz complementary metal oxide semiconductor transistor detector model

In this paper, we discuss the diffusion motion of carriers in the transistor channel in a terahertz frequency range, and propose an resistance-capacitance-inductance (RCL) model based on Boltzmann transport theory, and then put forward the rules to determine whether the diffusion part in the RCL model can be neglected for terahertz field-effect-transistor (FET) detectors. The traditional RCL model for FET detectors is based on classic kinetic theory. In this model only the drift and the scattering motion of the carrier density in transistor channel are considered, and the diffusion part is neglected without giving any explanation. To solve this problem, in this paper we adopt three steps: first, instead of classic kinetic theory, the equations of RCL transistor model including diffusion part are derived from Boltzmann transport equation, and by comparing the two models, the specific expression for the diffusion part is given. Second, the differences between the two models are calculated and simulated, including the conductivity in quasi-static mode and the current response in high frequency mode, with different gate voltages, temperatures and working frequencies. Third, combined with the 3 rules, the conditions to neglect the diffusion motion in the model are put forward. The results show that the diffusion motion of the carriers is caused by the inhomogeneity of the carrier density, affected by the gate voltage, the temperature and the changing speed of the carriers with respect to the local voltage. In quasi-static mode, the role of diffusion part will change with the gate voltage, and when the gate voltage equals threshold voltage (which is the best working point for transistor detector), the diffusion part cannot be neglected, for which the reason is that a larger gate voltage will lead to a smaller inhomogeneity of channel carrier density and then a weaker diffusion effect, thus the effect of diffusion conductance on the whole transistor conductance becomes smaller. For the terahertz-frequency working mode, the diffusion part will depend on temperature and frequency. With temperature increasing, the current responsivity difference caused by the diffusion part in the model slightly decreases; when the working frequency increases but below 1 THz, the diffusion part can be neglected; however, when the working frequency is above 1 THz, the transistor model should contain drift, scattering and diffusion part at the same time, for which the explanation is that when the temperature increases, the random thermal motion of the carrier becomes larger, thus the diffusion effect will be stronger; and if the frequency increases, the number of the carriers in one terminal of the channel will change faster, but due to the channel damping, the number of the carriers in another terminal will always be zero, thus the changing speed of the carrier density between the two terminals will be faster, then a larger inhomogeneity of carrier density and a stronger diffusion effect will appear. In conclusion, normally the transisitor works at the threshold gate voltage, and at this point, the diffusion effect in the channel will increase with working temperature and frequency increasing, thus the diffusion part in the model cannot be neglected. The results in this paper make a significant contribution to a more accurate terahertz transistor detector model.

Saturation of photoresponse to intense THz radiation in AlGaN/GaN HEMT detector

We report on the photoresponse of AlGaN/GaN high electron mobility transistors to the THz radiation of low (15 mW/cm2) and high (up to 40 kW/cm2) intensities. We show that the response can be described by the Dyakonov-Shur theory in the whole range of radiation intensity. At low intensities, the photoresponse is linear in radiation intensity. Under intense laser radiation, we observe a saturation at intensities >20 kW/cm2. We explain our results by the change of the channel conductivity under the influence of strong THz field. This mechanism of photoresponse saturation, which is due to the mobility decrease in high ac electric field, should exist for any type of field effect transistor detectors.

Terahertz 3D printed diffractive lens matrices for field-effect transistor detector focal plane arrays.

We present the concept, the fabrication processes and the experimental results for materials and optics that can be used for terahertz field-effect transistor detector focal plane arrays. More specifically, we propose 3D printed arrays of a new type - diffractive multi-zone lenses of which the performance is superior to that of previously used mono-zone diffractive or refractive elements and evaluate them with GaN/AlGaN field-effect transistor terahertz detectors. Experiments performed in the 300-GHz atmospheric window show that the lens arrays offer both a good efficiency and good uniformity, and may improve the signal-to-noise ratio of the terahertz field-effect transistor detectors by more than one order of magnitude. In practice, we tested 3 × 12 lens linear arrays with printed circuit board THz detector arrays used in postal security scanners and observed significant signal-to-noise improvements. Our results clearly show that the proposed technology provides a way to produce cost-effective, reproducible, flat optics for large-size field-effect transistor THz-detector focal plane arrays.

Improvement of terahertz field effect transistor detectors by substrate thinning and radiation losses reduction.

Phenomena of the radiation coupling to the field effect transistors based terahertz (THz) detectors are studied. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, is coupled to an antenna substrate leading to responsivity losses and/or cross-talk effects in the field effect based THz detector arrays. Experimental and theoretical investigations of the responsivity versus substrate thickness are performed. They clearly show how to minimize the losses by the detector/ array substrate thinning. In conclusion simple quantitative rules of losses minimization by choosing a proper substrate thickness of field effect transistor THz detectors are presented for common materials (Si, GaAs, InP, GaN) used in semiconductor technologies.