We present investigations of the fin-shaped GaN/AlGaN field effect transistors with two lateral Schottky barrier gates exactly placed on the edges of the fin-shaped transistor channel. We call this kind of FinFET modification the EdgeFET. It allowed us to efficiently control the current flow in two-dimensional electron gas conduction channel. We present experimental data of sub-THz detection by EdgeFETs. Control of the side gates allows changing the width of two-dimensional electron gas and forming a wire, as we expect should be beneficial for observation of terahertz plasma wave resonances. This paves the way towards future terahertz optopair using high-quality factor plasma wave resonances, for which it is necessary to eliminate oblique modes. We report also on the high-voltage, noise, and radio frequency (RF) performances of aluminium gallium nitride/gallium nitride (AlGaN/GaN) on silicon carbide (SiC) devices without any GaN buffer. Such a GaN–SiC hybrid material was developed in order to improve thermal management and to reduce trapping effects should be beneficial for observation of resonant emission.
KEYWORDS: Plasma, Field effect transistors, Terahertz radiation, Heterojunctions, Fin field effect transistors, Transistors, Terahertz detection, Gallium nitride, Temperature metrology
We report on the investigations of the fin-shaped GaN/AlGaN field effect transistors with two lateral Schottky barrier gates exactly placed on the edges of the fin-shaped transistor channel. This kind FinFET modification (EdgeFET) allowed us to efficiently control the current flow in two-dimensional electron gas conduction channel. We present experimental data of sub THz detection by EdgeFETs. We describe also how it is beneficial for observation of resonant plasma wave THz detection and emission.
We report on the investigations of the fin-shaped GaN/AlGaN field effect transistors (FinFETs) with two lateral Schottky barrier gates exactly placed at the edges of the fin-shaped transistor channel. This kind of FinFET modification (called EdgeFET) allowed us to efficiently control the current flow in two-dimensional electron gas conduction channel. Moreover, due to depletion, regions of the channel at a certain range of reverse bias form a nanowire, which is beneficial for the tunable resonant THz detection. Our studies of current-voltage characteristics and response in the sub-terahertz frequency range confirm the validity of the approach.
Fabrication of approx. 3 THz Al0.15Ga0.85As/GaAs QCLs grown by Molecular Beam Epitaxy equipped with Ta/Cu or Ti/Cu waveguide claddings will be presented.
Our previous studies showed that copper layers as the waveguide claddings are most promising in THz QCLs technology. The theoretical predictions showed that lasers with Ti/Cu or Ta/Cu claddings (where Ti and Ta play the role of diffusion barriers and improve adhesion) show the smallest waveguide losses when compared with other metals. The main important issue of the presentation will be the wafer bonding of the QCL active region and GaAs receptor wafer. We will compare the results of ex-situ and in-situ bonding technology. The structures were tested by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS). Our studies show that it was necessary to apply at least 5 nm-thick diffusion-barrier layers, as well as to keep all of the process temperatures below 400C in order to ensure the barrier tightness. The next important issue was control of composition of metallic claddings, in order to provide the control of the refractive index profiles of the claddings.
The ridge structure lasers were fabricated with ridge width in the range 100 – 140 µm, formed by dry plasma etching in BCl3/Cl2/Ar mixture in ICP RIE system.
The lasers operated with threshold current densities of approx. 1.2 kA/cm2 at 77 K and the Tmax = 130 K, when fed by 100-300 ns current pulses supplied with 0.3-1 kHz repetition frequencies.
*This research is supported by The National Centre for Research and Development (bilateral cooperation, project no. 1/POLTUR-1/2016) and TUBITAK (Scientific and Technical Research Council of Turkey) project number 215E113.
We report research results with regard to AlGaAs/GaAs structure processing for THz quantum-cascade lasers (QCLs). We focus on the processes of Ti/Au cladding fabrication for metal–metal waveguides and wafer bonding with indium solder. Particular emphasis is placed on optimization of technological parameters for the said processes that result in working devices. A wide range of technological parameters was studied using test structures and the analysis of their electrical, optical, chemical, and mechanical properties performed by electron microscopic techniques, energy dispersive x-ray spectrometry, secondary ion mass spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and circular transmission line method. On that basis, a set of technological parameters was selected for the fabrication of devices lasing at a maximum temperature of 130 K from AlGaAs/GaAs structures grown by means of molecular beam epitaxy. Their resulting threshold-current densities were on a level of 1.5 kA/cm2. Furthermore, initial stage research regarding fabrication of Cu-based claddings is reported as these are theoretically more promising than the Au-based ones with regard to low-loss waveguide fabrication for THz QCLs.
We report our research on processing of AlGaAs/GaAs structures for THz quantum-cascade lasers (QCLs). We focus on
the processes of fabrication of Ti/Au claddings for metal-metal waveguides and the wafer bonding with indium solder.
We place special emphasis on the optimum technological conditions of these processes, leading to working devices. The
wide range of technological conditions was studied, by use of test structures and analyses of their electrical, optical,
chemical and mechanical properties, performed by electron microscopic techniques, energy dispersive X-ray
spectrometry, secondary ion mass spectroscopy, atomic force microscopy, fourier-transform infra-red spectroscopy and
circular transmission line method. On the basis of research a set of technological conditions was selected, and devices
lasing at the maximum temperature 130K were fabricated from AlGaAs/GaAs structures grown by molecular beam
epitaxy (MBE) technique. Their threshold-current densities were about 1.5kA/cm2. Additionally we report our initial
stage research on fabrication of Cu-based claddings, that theoretically are more promising than the Au-based ones for
fabrication of low-lossy waveguides for THz QCLs.
In this work, we study the nature of long-lived photoexcitations in intercalated, partially and
predominantly non-intercalated semicrystalline poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno
[3,2,-b]thiophene) (pBTTT):phenyl-C61 -butyric acid methyl ester (PC61BM) blend films by
quasi-steady-state photoinduced absorption (PIA) spectroscopy. We find that polarons are generated in
these microstructures. However, the polarons generated in partially and predominantly non-intercalated
films (1.7 eV) are at higher energy than in intercalated film (1.4 eV). After comparing with the polaron
generation in neat pBTTT polymer film, we propose that the polarons generated in partially and
predominantly non-intercalated film are delocalized charges, and the polarons generated in intercalated
film are localized charges. Furthermore, we also find that the polarons generated in the partially
non-intercalated film have the longest lifetime.
Polymeric semiconductors such has regioregular poly(3-hexylthiophene) have electronic proprieties that can be tuned by proper control of the solid-state microstructure. We process thin films of P3HT of different molecular weight ranging from 2 kg/mol to 341 kg/mol. The polymer undergo a transition from a paraffinic, non-entangled microstructure to a two-phase microstructure defined by entangled chains embedded in amorphous regions at around 50 kg/mol. We observe an abrupt decrease in the intermolecular coupling from an average of ~20 meV for molecular weight below 50 kg/mol to ~5 meV above 50 kg/mol. We assign this decrease in the interchain coupling and associated free-exciton bandwidth at higher molecular weight to a transition from a one-phase morphology to a two-phase morphology defined above. In steady-state photoluminescence, we associate the lower Huang-Rhys factors at higher molecular weight to more planar backbone.
AlGaN/GaN based FETs have great potential as sensitive and fast operating detectors because of their material
advantages such as high breakdown voltage, high electron mobility, and high saturation velocity. These advantages could
be exploited for resonant and non-resonant terahertz detection. We have designed, fabricated, and characterized
AlGaN/GaN based FETs as single pixel terahertz detectors. This work focuses on non-resonant detection and imaging
using GaN field plate FETs. To evaluate their performances as terahertz detectors, we have measured the responsivity as
a function of gate voltage, the azimuthal angle between the terahertz electric field, the source-to-drain direction, and the
temperature. A simple 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 and it fully describes the experimental results on the non-resonant sub-terahertz
detection by the AlGaN/GaN based FETs. The imaging performances are evaluated by scanning objects in transmission
mode and an example of application of terahertz imaging as new non-destructive technique for the quality control of
materials is given. Results indicate that these FETs can be considered as promising devices for terahertz detection and
imaging applications.
In organic photovoltaic diodes, singlet intrachain excitons dissociate into geminate polaron pairs (GPP) at the
heterojonction, which further dissociate into photocarriers or relax into charge transfer exciton (CTX) states. Our
temperature-dependent, time-resolved spectroscopic approach unravels the dynamics of those species in films of polycarbazole/fullerene derivative blend. We find that GPP act as a dark reservoir that feeds the CTX. At low temperature, the GPP are trapped and feed the CTX via tunneling, but not the free photocarriers. At room temperature, some of the GPP can overcome the Coulomb barrier and feed the CTX promptly, or be deeply trapped and feed the CTX on several timescales. We find that at room temperature, 16% of the geminate recombination is accounted for by trapped geminate polaron pairs.
W. Knap, F. Teppe, C. Consejo, B. Chenaud, J. Torres, P. Solignac, Z. Wasilewski, M. Zholudev, N. Dyakonova, D. Coquillat, P. Buzatu, A. El Fatimy, F. Schuster, H. Videlier, M. Sakowicz, B. Giffard, T. Skotnicki, F. Palma
In this work we review the most important results concerning the physics and applications of FETs as Terahertz
detectors. We present two experiments showing: i) Terahertz detection based on low cost 130 nm silicon
technology Field Effect Transistors in the sub-THz range (0.2 THz up to 1.1 THz) and ii) first results on
detection by FETs of emission from 3.1 THz Quantum Cascade Lasers.
We report on active imaging with CMOS transistors at 300 GHz and 1.05 THz. Two basic focal plane arrays consisting
of nMOS transistors and wide-band bow-tie antennas have been implemented in a low-cost 130 nm CMOS technology.
Raster scan imaging of objects concealed in a paper envelope has been achieved at 300 GHz with a commercial radiation
source. The images clearly reveal the concealed objects with a dynamic range of 35 dB and a resolution of 3 mm. At
1.05 THz, the pixels achieve a responsivity of 50 V/W and a noise equivalent power of 900 pW/Hz0.5.
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