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We present technology computer-aided design (TCAD) models for AlGaAs/InGaAs and AlGaN/GaN and silicon TeraFETs, plasmonic field effect transistors (FETs), for terahertz (THz) detection validated over a wide dynamic range. The modeling results are in good agreement with the experimental data for the AlGaAs/InGaAs heterostructure FETs (HFETs) and, to the low end of the dynamic range, with the analytical theory of the TeraFET detectors. The models incorporate the response saturation effect at high intensities of the THz radiation observed in experiments and reveal the physics of the response saturation associated with different mechanisms for different material systems. These mechanisms include the gate leakage, the velocity saturation and the avalanche effect.
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Terahertz (THz) response of transistor and integrated circuit yields important information about device parameters and has been used for distinguishing between working and defective transistors and circuits. Using a TCAD model for SiGe HBTs we simulate their current-voltage characteristics and their response to sub-THz (300,GHz) radiation. Applying different mixed mode schemes in TCAD, we simulated the dynamic range of the THz response for SiGe HBTs and showed that it is comparable with that of the TeraFET detectors. The HBT response to the variations of the detector design parameters are investigated at different frequencies with the harmonic balance simulation in TCAD. These results are useful for the physical design and optimization for the HBT THz detectors and for the identification of faulty SiGe HBT and Si BiCMOS circuits using sub-THz or THz scanning.
We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state of the art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers in continuous wave, with a maximum optical output power of 4 mW (0.73 mW in the comb regime). Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime extending over a continuous 106 mA current range (current density dynamic range of 1.24), significantly larger than the state of the art reported under similar geometries, with a corresponding emission bandwidth of 1.05 THz ans a stable and narrow (4.15 KHz) beatnote detected with a signal-to-noise ratio of 34 dB. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 MHz/mA and 2.1 MHz/mA and a temperature-tuning coefficient of -4 MHz/K. The ability to tune the THz QCL combs over their full dynamic range by temperature and current paves the way for their use as powerful spectroscopy tool that can provide broad frequency coverage combined with high precision spectral accuracy.
A 64-channel mixed-mode ASIC, suitable for particle detectors of large dynamic range and high capacitance up to hundreds of pF, is presented here. Each channel features an analogue front-end for signal amplification and filtering, and a mixed signal back-end to digitise and store the signal information. The analogue part consists of a low input-impedance programmable gain pre-amplifier based on a regulated common-gate (RCG) input stage, two shapers optimised for time and energy measurements. The back-end part mainly includes discriminators, TDCs and ADCs, which are used to process the signal and encode both the time of arrival and the charge in the input signal with a fully digital output. The programmable gain of the front-end (up to 400 fC input dynamic range) and the versatile back-end allow the readout of different gaseous detectors like GEM, MicroMEGAS and MWPC. The ASIC is designed for an event rate up to 100 kHz per channel and a power consumption less than 9 mW/channel, has been fabricated in a 110 nm CMOS technology.
The coherent manipulation of acoustic waves on the nanoscale usually requires multilayers with thicknesses and interface roughness defined down to the atomic monolayer. This results in expensive devices with predetermined functionality. Nanoscale mesoporous materials present high surface-to-volume ratio and tailorable mesopores, which allow the incorporation of chemical functionalization to nanoacoustics. However, the presence of pores with sizes comparable to the acoustic wavelength is intuitively perceived as a major roadblock in nanoacoustics. Here we present multilayered nanoacoustic resonators based on mesoporous SiO$_2$ thin-films showing acoustic resonances in the 5-100 GHz range. We characterize the acoustic response of the system using coherent phonon generation experiments. Despite resonance wavelengths comparable to the pore size, we observe for the first time unexpectedly well-defined acoustic resonances with Q-factors around 10. Our results open the path to a promising platform for nanoacoustic sensing and reconfigurable acoustic nanodevices based on soft, inexpensive fabrication methods.
This study presents a fabrication process for lithium-drifted silicon (Si(Li)) detectors that, compared to previous methods, allows for mass production at a higher yield, while providing a large sensitive area and low leakage currents at relatively high temperatures. This design, developed for the unique requirements of the General Antiparticle Spectrometer (GAPS) experiment, has an overall diameter of 10 cm, with ~9 cm of active area segmented into 8 readout strips, and an overall thickness of 2.5 mm, with $gtrsim$2.2 mm ($gtrsim$90%) sensitive thickness. An energy resolution $lesssim$4 keV full-width at half-maximum (FWHM) for 20-100 keV X-rays is required at the operating temperature ~-40C, which is far above the liquid nitrogen temperatures conventionally used to achieve fine energy resolution. High-yield production is also required for GAPS, which consists of $gtrsim$1000 detectors. Our specially-developed Si crystal and custom methods of Li evaporation, diffusion and drifting allow for a thick, large-area and uniform sensitive layer. We find that retaining a thin undrifted layer on the p-side of the detector drastically reduces the leakage current, which is a dominant component of the energy resolution at these temperatures. A guard-ring structure and optimal etching of the detector surface are also confirmed to suppress the leakage current. We report on the mass production of these detectors that is ongoing now, and demonstrate it is capable of delivering a high yield of ~90%.
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