Nanowire-based field effect transistors for terahertz detection and imaging systems

Hybrid Dirac semimetal-based photodetector with efficient low-energy photon harvesting

Despite the considerable effort, fast and highly sensitive photodetection is not widely available at the low-photon-energy range (~meV) of the electromagnetic spectrum, owing to the challenging light funneling into small active areas with efficient conversion into an electrical signal. Here, we provide an alternative strategy by efficiently integrating and manipulating at the nanoscale the optoelectronic properties of topological Dirac semimetal PtSe₂ and its van der Waals heterostructures. Explicitly, we realize strong plasmonic antenna coupling to semimetal states near the skin-depth regime (λ/10⁴), featuring colossal photoresponse by in-plane symmetry breaking. The observed spontaneous and polarization-sensitive photocurrent are correlated to strong coupling with the nonequilibrium states in PtSe₂ Dirac semimetal, yielding efficient light absorption in the photon range below 1.24 meV with responsivity exceeding ∼0.2 A/W and noise-equivalent power (NEP) less than ~38 pW/Hz^0.5, as well as superb ambient stability. Present results pave the way to efficient engineering of a topological semimetal for high-speed and low-energy photon harvesting in areas such as biomedical imaging, remote sensing or security applications.

Semiconductor Nanowire Field-Effect Transistors as Sensitive Detectors in the Far-Infrared

Engineering detection dynamics in nanoscale receivers that operate in the far infrared (frequencies in the range 0.1-10 THz) is a challenging task that, however, can open intriguing perspectives for targeted applications in quantum science, biomedicine, space science, tomography, security, process and quality control. Here, we exploited InAs nanowires (NWs) to engineer antenna-coupled THz photodetectors that operated as efficient bolometers or photo thermoelectric receivers at room temperature. We controlled the core detection mechanism by design, through the different architectures of an on-chip resonant antenna, or dynamically, by varying the NW carrier density through electrostatic gating. Noise equivalent powers as low as 670 pWHz-1/2 with 1 µs response time at 2.8 THz were reached.

Sensitivity of Field-Effect Transistor-Based Terahertz Detectors

This paper presents an overview of the different methods used for sensitivity (i.e., responsivity and noise equivalent power) determination of state-of-the-art field-effect transistor-based THz detectors/sensors. We point out that the reported result may depend very much on the method used to determine the effective area of the sensor, often leading to discrepancies of up to orders of magnitude. The challenges that arise when selecting a proper method for characterisation are demonstrated using the example of a 2×7 detector array. This array utilises field-effect transistors and monolithically integrated patch antennas at 620 GHz. The directivities of the individual antennas were simulated and determined from the measured angle dependence of the rectified voltage, as a function of tilting in the E- and H-planes. Furthermore, this study shows that the experimentally determined directivity and simulations imply that the part of radiation might still propagate in the substrate, resulting in modification of the sensor effective area. Our work summarises the methods for determining sensitivity which are paving the way towards the unified scientific metrology of FET-based THz sensors, which is important for both researchers competing for records, potential users, and system designers.

Review on III-V Semiconductor Single Nanowire-Based Room Temperature Infrared Photodetectors

Recently, III-V semiconductor nanowires have been widely explored as promising candidates for high-performance photodetectors due to their one-dimensional morphology, direct and tunable bandgap, as well as unique optical and electrical properties. Here, the recent development of III-V semiconductor-based single nanowire photodetectors for infrared photodetection is reviewed and compared, including material synthesis, representative types (under different operation principles and novel concepts), and device performance, as well as their challenges and future perspectives.

Biological applications of terahertz technology based on nanomaterials and nanostructures

Terahertz (THz) technology is now drawing increasing attention around the world; it has been considered as an efficient non-destructive, non-contact and label-free optical method for biological detection. In this field, nanomaterials and nanostructures have been constantly advancing the development of THz technology. Here, we proposed some latest applications of nanotechnology to improve THz biological detection capability for providing progressive THz systems, thus enabling outstanding detection performance utilizing THz spectroscopy and imaging; these will encourage broader interest in various fields. The uniqueness, limitations, and future prospects of THz biological applications based on nanomaterials and nanostructures will also be reviewed in light of recent developments.

Improving the electrical properties of InAs nanowire field effect transistors by covering them with Y2O3/HfO2 layers

Quasi-one-dimensional semiconducting materials have attracted increasing attention due to their excellent ability to downscale the size of transistors. However, in quasi-one-dimensional nanowire (NW) transistors, their surface and interface properties play a very important role mainly due to the large surface-to-volume ratio of NWs and surface scattering, which degrade their carrier mobility. Herein, we developed a new method to cover the channel surface of InAs NW field effect transistors (FETs) with Y₂O₃/HfO₂ layers to improve their electrical properties. We successfully fabricated nine FETs and measured their electrical properties, which improve after depositing the Y₂O₃/HfO₂ layers, including an increase in on-state current, decrease in off-state current, increase in transconductance, increase in electron mobility and decrease in subthreshold swing. By comparing the properties of Y₂O₃/HfO₂-covered devices with that of the FETs fabricated without the Y₂O₃ covering or without annealing, we prove that it is the combined Y₂O₃/HfO₂ layers instead of only the Y₂O₃ or HfO₂ layer that improve the electrical properties of the FETs. The Cs-corrected high-resolution scanning transmission electron microscopy study demonstrates that Y can actually diffuse through the native oxide layer (confirmed to be InO_x) and reach the surface of the InAs NWs. Our results indicate that the desirable characteristics of Y₂O₃ and the surface passivation by HfO₂ improve the electrical properties of the InAs NW FETs, in which Y₂O₃ plays an important role to modify and stabilize the interface between the InAs NWs and the outside dielectric layer. Furthermore, this method should also be applicable to other III-V materials.

Single n+-i-n+ InP nanowires for highly sensitive terahertz detection

Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n⁺-i-n⁺ InP nanowires. The axial doping profile of the n⁺-i-n⁺ InP nanowires has been calibrated and characterized using combined optical and electrical approaches to achieve nanowire devices with low contact resistances, on which the highly-sensitive InP single-nanowire photoconductive THz detectors have been demonstrated. While the n⁺-i-n⁺ InP nanowire detector has a only pA-level response current, it has a 2.5 times improved signal-to-noise ratio compared with the undoped InP nanowire detector and is comparable to traditional bulk THz detectors. This performance indicates a promising path to nanowire-based THz electronics for future commercial applications.

Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm(2) V(-1) s(-1)) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.

Low ensemble disorder in quantum well tube nanowires

We have observed very low disorder in high quality quantum well tubes (QWT) in GaAs-Al(0.4)Ga(0.6)As core-multishell nanowires. Room-temperature photoluminescence spectra were measured from 150 single nanowires enabling a full statistical analysis of both intra- and inter-nanowire disorder. By modelling individual nanowire spectra, we assigned a quantum well tube thickness, a core disorder parameter and a QWT disorder parameter to each nanowire. A strong correlation was observed between disorder in the GaAs cores and disorder in the GaAs QWTs, which indicates that variations in core morphology effectively propagate to the shell layers. This highlights the importance of high quality core growth prior to shell deposition. Furthermore, variations in QWT thicknesses for different facet directions was found to be a likely cause of intra-wire disorder, highlighting the need for accurate shell growth.

Single nanowire photoconductive terahertz detectors

Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as diverse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors.

Nanowire Terahertz detectors with a resonant four-leaf-clover-shaped antenna

We report on the development of an innovative class of nanowire-based Terahertz (THz) detectors in which the metamaterial properties of an antenna have been imported in the detection scheme of an overdamped plasma-wave field-effect transistor making its response resonant to THz radiation. Responsivities of ~105 V/W at 0.3 THz, with noise equivalent power levels ≈ 10(-10) W/√Hz, detectivities ~2 · 10(8) cm√Hz/W and quantum efficiencies ~1.2 · 10(-5) are reached at room-temperature. The resonant nature of the detection scheme provided by the four-leaf-clover-shaped geometry and the possibility to extend this technology to large multi-pixel arrays opens the path to demanding applications for ultra-sensitive metrology, spectroscopy and biomedicine.

Quartz-enhanced photoacoustic spectroscopy: a review

A detailed review on the development of quartz-enhanced photoacoustic sensors (QEPAS) for the sensitive and selective quantification of molecular trace gas species with resolved spectroscopic features is reported. The basis of the QEPAS technique, the technology available to support this field in terms of key components, such as light sources and quartz-tuning forks and the recent developments in detection methods and performance limitations will be discussed. Furthermore, different experimental QEPAS methods such as: on-beam and off-beam QEPAS, quartz-enhanced evanescent wave photoacoustic detection, modulation-cancellation approach and mid-IR single mode fiber-coupled sensor systems will be reviewed and analysed. A QEPAS sensor operating in the THz range, employing a custom-made quartz-tuning fork and a THz quantum cascade laser will be also described. Finally, we evaluated data reported during the past decade and draw relevant and useful conclusions from this analysis.