scholarly journals Effect of the Front and Back Illumination on Sub-Terahertz Detection Using n-Channel Strained-Silicon MODFETs

2020 ◽  
Vol 10 (17) ◽  
pp. 5959
Author(s):  
Juan A. Delgado-Notario ◽  
Jaime Calvo-Gallego ◽  
Jesús E. Velázquez-Pérez ◽  
Miguel Ferrando-Bataller ◽  
Kristel Fobelets ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Thz Radiation ◽  
Strained Si ◽  
Wave Source ◽  
Electromagnetic Simulations ◽  
Terahertz Detection ◽  
Bonding Wires ◽  
Bottom Side ◽  
Photovoltaic Mode ◽  
Efficient Coupling

Plasma waves in semiconductor gated 2-D systems can be used to efficiently detect Terahertz (THz) electromagnetic radiation. This work reports on the response of a strained-Si Modulation-doped Field-Effect Transistor (MODFET) under front and back sub-THz illumination. The response of the MODFET has been characterized using a two-tones solid-state continuous wave source at 0.15 and 0.30 THz. The DC drain-to-source voltage of 500-nm gate length transistors transducing the sub-THz radiation (photovoltaic mode) exhibited a non-resonant response in agreement with literature results. Two configurations of the illumination were investigated: (i) front side illumination in which the transistor was shined on its top side, and (ii) back illumination side where the device received the sub-THz radiation on its bottom side, i.e., on the Si substrate. Under excitation at 0.15 THz clear evidence of the coupling of terahertz radiation by the bonding wires was found, this coupling leads to a stronger response under front illumination than under back illumination. When the radiation is shifted to 0.3 THz, as a result of a lesser efficient coupling of the EM radiation through the bonding wires, the response under front illumination was considerably weakened while it was strengthened under back illumination. Electromagnetic simulations explained this behavior as the magnitude of the induced electric field in the channel of the MODFET was considerably stronger under back illumination.

scholarly journals Numerical Study of the Coupling of Sub-Terahertz Radiation to n-Channel Strained-Silicon MODFETs

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 688
Author(s):  
Jaime Calvo-Gallego ◽  
Juan A. Delgado-Notario ◽  
Jesús E. Velázquez-Pérez ◽  
Miguel Ferrando-Bataller ◽  
Kristel Fobelets ◽  
...  
Keyword(s):  
Electric Field ◽  
Continuous Wave ◽  
Numerical Study ◽  
Three Dimensional ◽  
Thz Radiation ◽  
Internal Electric Field ◽  
Strained Si ◽  
Transistor Channel ◽  
Electromagnetic Simulations ◽  
Bonding Wires

This paper reports on a study of the response of a T-gate strained-Si MODFETs (modulation-doped field-effect transistor) under continuous-wave sub-THz excitation. The sub-THz response was measured using a two-tones solid-state source at 0.15 and 0.30 THz. The device response in the photovoltaic mode was non-resonant, in agreement with the Dyakonov and Shur model for plasma waves detectors. The maximum of the photoresponse was clearly higher under THz illumination at 0.15 THz than at 0.3 THz. A numerical study was conducted using three-dimensional (3D) electromagnetic simulations to delve into the coupling of THz radiation to the channel of the transistor. 3D simulations solving the Maxwell equations using a time-domain solver were performed. Simulations considering the full transistor structure, but without taking into account the bonding wires used to contact the transistor pads in experiments, showed an irrelevant role of the gate length in the coupling of the radiation to the device channel. Simulations, in contradiction with measurements, pointed to a better response at 0.3 THz than under 0.15 THz excitation in terms of the normalized electric field inside the channel. When including four 0.25 mm long bonding wires connected to the contact pads on the transistor, the normalized internal electric field induced along the transistor channel by the 0.15 THz beam was increased in 25 dB, revealing, therefore, the important role played by the bonding wires at this frequency. As a result, the more intense response of the transistor at 0.15 THz than at 0.3 THz experimentally found, must be attributed to the bonding wires.

scholarly journals Off-Axis Diffractive Optics for Compact Terahertz Detection Setup

2020 ◽  
Vol 10 (23) ◽  
pp. 8594
Author(s):  
Paweł Komorowski ◽  
Mateusz Surma ◽  
Michał Walczakowski ◽  
Przemysław Zagrajek ◽  
Agnieszka Siemion
Keyword(s):  
3D Printing ◽  
Small Volume ◽  
Optical Element ◽  
Structure Design ◽  
Thz Radiation ◽  
Direct Printing ◽  
Terahertz Detection ◽  
3D Printed ◽  
Printing Techniques ◽  
Optical Structure

Medical and many other applications require small-volume setups enabling terahertz imaging. Therefore, we aim to develop a device for the in-reflection examination of the samples. Thus, in this article, we focus on the diffractive elements for efficient redirection and focusing of the THz radiation. A terahertz diffractive optical structure has been designed, optimized, manufactured (using extrusion-based 3D printing) and tested. Two manufacturing methods have been used—direct printing of the structures from PA12, and casting of the paraffin structures out of 3D-printed molds. Also, the limitations of the off-axis focusing have been discussed. To increase the efficiency, an iterative algorithm has been proposed that optimizes off-axis structures to focus the radiation into small focal spots located far from the optical axis, at an angle of more than 30 degrees. Moreover, the application of higher-order kinoform structure design allowed the maintaining of the smallest details of the manufactured optical element, using 3D printing techniques.

scholarly journals Dynamical theory calculations of spin-echo resolved grazing-incidence scattering from a diffraction grating

2010 ◽  
Vol 43 (3) ◽  
pp. 455-465 ◽  
Author(s):  
Rana Ashkar ◽  
P. Stonaha ◽  
A. L. Washington ◽  
V. R. Shah ◽  
M. R. Fitzsimmons ◽  
...  
Keyword(s):  
Diffraction Grating ◽  
Continuous Wave ◽  
Spin Echo ◽  
Grazing Incidence ◽  
Grating Period ◽  
Dynamical Theory ◽  
Neutron Spin ◽  
Wave Source ◽  
Rectangular Profile ◽  
Good Account

Neutrons scattered or reflected from a diffraction grating are subject to a periodic potential analogous to the potential experienced by electrons within a crystal. Hence, the wavefunction of the neutrons can be expanded in terms of Bloch waves and a dynamical theory can be applied to interpret the scattering phenomenon. In this paper, a dynamical theory is used to calculate the results of neutron spin-echo resolved grazing-incidence scattering (SERGIS) from a silicon diffraction grating with a rectangular profile. The calculations are compared with SERGIS measurements made on the same grating at two neutron sources: a pulsed source and a continuous wave source. In both cases, the spin-echo polarization, studied as a function of the spin-echo length, peaks at integer multiples of the grating period but there are some differences between the two sets of data. The dynamical theory explains the differences and gives a good account of both sets of results.

scholarly journals High efficiency photomodulators for millimeter wave and THz radiation

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
I. R. Hooper ◽  
N. E. Grant ◽  
L. E. Barr ◽  
S. M. Hornett ◽  
J. D. Murphy ◽  
...  
Keyword(s):  
High Efficiency ◽  
Continuous Wave ◽  
Broad Band ◽  
Cost Effective ◽  
Silicon Wafers ◽  
Thz Radiation ◽  
Limiting Factor ◽  
Switching Speed ◽  
Carrier Lifetimes ◽  
Narrow Frequency Band

AbstractPhotomodulators for mm-wave and THz radiation are an essential component for many imaging and signal processing applications. While a myriad of schemes have been devised to enhance photomodulation by enhancing the light-matter interaction, there has been less focus on the photoconductive materials themselves, which are often the limiting factor. Here, we present an approach to increase the photomodulation efficiency of silicon by orders of magnitude, using post treatment of off-the-shelf silicon wafers. The increase in efficiency removes the need for bulky and costly amplified laser sources, and creates the potential for compact and cost-effective modulators for real-world applications. By passivating the surfaces of long bulk-lifetime silicon wafers with Al2O3, the recombination of the photoexcited carriers at the surfaces is mostly eliminated. This results in vastly longer excess carrier lifetimes (up to ~50 ms), with corresponding increases in photoconductivity. The resulting modulators are highly efficient, with the transmission through them being reduced from ~90% to <10% over a narrow frequency band with a continuous wave excitation intensity of just 10 Wm−2, whilst modulation factors of greater than 80% can be achieved over a broad band with similar intensities. We also discuss the limitations of such long-lifetime modulators for applications where the switching speed or spatial resolution of a modulator may be critical.

scholarly journals Terahertz Frequency Continuous-Wave Spectroscopy and Imaging of Explosive Substances

ISRN Optics ◽  
2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Michael A. Startsev ◽  
Abdulhakem Y. Elezzabi
Keyword(s):  
Continuous Wave ◽  
Solid Phase ◽  
Spectral Characteristics ◽  
Thz Radiation ◽  
Line Broadening ◽  
Experimental Conditions ◽  
Explosive Materials ◽  
Raster Scan ◽  
Security Screenings ◽  
Frequency Radiation

Continuous-wave terahertz (THz) radiation spectroscopy was performed on high explosive materials using a tuneable optical parametric oscillator (OPO). Military grade, solid-phase, explosive substances, such as cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), pentaerythritol tetranitrate (PETN), and composition-4, were spectrally scanned over the 0.7–1.9 THz frequency range under experimental conditions modeling that of “real-world” security screenings. Spectral peak locations and spectral line broadening effects were quantified using a Lorentz lineshape fit algorithm. The full-width half-maximum (FWHM) parameter computed by the Lorentz fit algorithm was shown to help in the identification of samples with broad and sparse spectral characteristics. A concealed explosives identification scheme was demonstrated through raster scan THz frequency radiation imaging at specific OPO tuning frequencies.

Sign in / Sign up

Export Citation Format

Share Document