1,721,084 research outputs found
Dependence of Static and Dynamic GaN HEMT Characteristics from Fe-doped GaN Buffer Parameters
No full textThe influence of Fe-doped buffer parameters on the static and dynamic characteristics of GaN HEMTs have been analyzed by means of two-dimensional numerical simulations. Results obtained on the static characteristics of the simulated devices have shown that thick and highly doped buffers yield better performances in terms of device output conductance and subthreshold conduction, while leaving mainly unaffected other DC parameters. On the other hand, when dynamic characteristics are evaluated, a significant current collapse has been observed pointing out the importance of the correct design of Fe-doped buffer parameters in order to obtain state-of-the-art GaN HEMT performances
The effect of gate and recess scaling on the gate-drain breakdown and hot-electron reliability of AlGaAs/GaAs power HFETs
No full textInfluence of substrate on the performances of semi-insulating GaAs detectors
No full textA study of the carrier transport mechanism, the charge collection efficiency and the energy resolution has been carried out on semi-insulating GaAs X-ray detectors realised on substrates with concentrations of acceptor dopants N-a, varying from 10(14) to 10(17) cm(-3). The electron collection efficiency (ECE) and the reverse current were found to decrease with increasing N-a, while the resistivity of the material was found to increase. At room temperature, the best collection efficiency (95%) and the best energy resolution (13.7 keV FWHM) for 59.5 keV X-rays of the Am-241 source, have been achieved with the less doped detectors (N-1 - 10(14) cm(-3)). The concentrations of ionised EL2(+), determined by optical measurements in IR regions, was shown to increase with N-a and to be quasi-inversely proportional to the ECE values. This behaviour strongly supports the hypothesis that the EL2 defects play a main role in the compensation of the material and in the limitation of the detection properties. (C) 2000 Published by Elsevier Science B.V. All rights reserved
Correlation Between Surface-state Density and Impact Ionization Phenomena In Gaas-mesfets
No full textGaAs MESFET's passivated with PECVD SiN show a lower surface-state density in comparison with SiO passivated devices, as deduced from g(m)(f) dispersion curves. Lower carrier multiplication due to impact ionization phenomena in the active channel and consequently a higher breakdown voltage are observed in SiO passivated samples. These effects are attributed to a lower peak electric field near the drain edge of the gate, deriving from an accumulation of negative surface charge
Frequency dispersion of transconductance: a tool to characterise deep levels in III-V FETs
No full textFrequency dispersion of transconductance g(m)(f) has been exploited to quantitatively investigate the properties of deep traps in III-V FET devices, namely DX centres in GaAs/AlGaAs HEMTs. This method requires simple data acquisition and elaboration and is applied directly to packaged devices. Thermal emission energy E(a) = 0.46 eV and capture cross-section sigma = 3.10(-14) cm2 have been obtained for DX centers in AlGaAs, in good agreement with published data. By increasing V(DS), we measured also an E(a) decrease due to hot electron trapping by the DX centres
Epitaxial silicon carbide charge particle detectors
No full textThe radiation detection properties of Schottky detectors made on epitaxial layers of 4H silicon carbide were evaluated. Exposure to 5.48 MeV alpha particles from a Am-241 source in vacumn led to robust signals from the detectors. The collection of the charge carriers was found to increase linearly with the square root of the applied reverse bias. (C) 1999 Elsevier Science B.V. All rights reserved
Impact Ionization In Gaas-mesfets - Comments
No full textIn the above-named work (see ibid., vol.11, p.113-15, March 1990), Hui et al. proposed a method to measure impact ionization current in GaAs MESFETs and evaluated the impact ionization coefficient alpha /sub n/ in GaAs. For electric fields greater than approximately 1.5*10/sup 5/ V-cm/sup -1/, alpha /sub n/ can be fitted to the equation alpha /sub n/=4.0*10/sup 6/*exp (-2.3*10/sup 6//E). In the present work, the commenters performed careful measurements of gate current I/sub g/ in GaAs MESFET devices similar to those used by Hui et al., and they show that the ionization coefficient still fits the above equation down to alpha /sub n/=10/sup -4/ cm/sup -1/. These results extend the previous data by three orders of magnitude. In a reply, the original authors affirm that the commenters have significantly improved the accuracy of the data previously presented
Silicon Carbide Detector for Laser-Generated Plasma Radiation
No full textWe present the performance of a Silicon Carbide (SiC) detector in the acquisition of the radiation emitted by laser generated plasmas. The detector has been employed in time of flight (TOF) configuration within an experiment performed at the Prague Asterix Laser System (PALS). The detector is a 5 mm(2) area 100 nm thick circular Ni-SiC Schottky junction on a high purity 4H-SiC epitaxial layer 115 mu m thick. Current signals from the detector with amplitudes up to 1.6 A have been measured, achieving voltage signals over 80 V on a 50 Omega load resistance with excellent signal to noise ratios. Resolution of few nanoseconds has been experimentally demonstrated in TOF measurements. The detector has operated at 250 V DC bias under extreme operating conditions with no observable performance degradation
Schottky Junctions on Semi-Insulating LEC Gallium Arsenide for X and Gamma Ray Spectrometers operated at and below Room Temperature
No full textThis work deals with the study of a Schottky junction used as an X- and 7-ray detector in a spectrometer operated in the temperature range from -30 °C to +22 C. The device (7 mm2 active area and 100 /urn thickness), fabricated on liquid encapsulated Czochralski (LEG) semi-insulating Gallium Arsenide, is designed with a noninjecting ohmic contact which allows biasing voltages up to 550 V. At room temperature (22 °C) the energy resolution is found to be relatively poor (15.5-keV full-width at half-maximum (FWHM) at 59.5 keV) due to the large junction reverse current, whose density (7-37 nA/mm2 at Vbias -100-500 V) is within the typical values for Schottky junctions on SI LEG GaAs. By cooling of the detector to -30 °C, the noise of the reverse current is drastically lowered, thus achieving electronic noise levels around 160-180 rms electrons (1.6-1.8 keV FWHM). At 500-V bias, the 241Am spectrum has been resolved down to an energy of 4 keV with charge collection efficiency of cce 97% and a resolution of about 2-keV FWHM for the Np L lines and 2.4-keV FWHM for the 59.5-keV 7 photons. The linearity of the detector has been measured to be better than ±0.6% within the explored energy range (14-59 keV). From the experimental spectra, it has been analyzed how either the electronic noise or the trapping of the signal charge contribute to the energy resolution of the spectrometer. The result is that despite the high measured cce, the trapping gives a contribution higher than 1.5keV FWHM for the 59.5-keV spectral line. A comparison between the experimental results and Monte Carlo simulations, based on the Hecht model of charge trapping in detectors, is shown to give a satisfactory justification of the observed phenomena. A total mean drift length of carriers has been experimentally derived, finding an exponential dependence upon the bias voltage applied to the detector
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