Enhancement/depletion PHEMT device

An embodiment of the present invention concerns a layered epitaxial structure for enhancement/ depletion PHEMT devices, an enhancement/depletion PHEMT device and a method for manufacturing an enhancement/ depletion PHEMT device that finds advantageous, but not exclusive, application in the manufacturing of integrated circuits operating at millimeter-Wave and microWave frequencies

Enhancement-/depletion-PHEMT device and manufacturing method thereof

The present invention relates, in general, to enhancement/ depletion Pseudomorphic High Electron Mobility Transistors (PHEMTs) and, in particular, to an enhancement/depletion PHEMT device and a method for manufacturing enhancement/depletion PHEMT devices that finds advantageous, but not exclusive, application in the production of integrated circuits operating at millimetre-wave and microwave frequencies

Investigation of Ni/4H-SiC diodes as radiation detectors with low doped n-type 4H-SiC epilayers

Abstract The development of SiC minimum ionising particle (MIP) detectors imposes severe constrains in the electronic quality and the thickness of the material due to the relatively high value of the energy required to produce an electron–hole pair in this material by MIP against the value for Si. In this work, particle detectors were made using semiconductor epitaxial undoped n-type 4H-SiC as the detection medium. The thickness of the epilayer is on the order of 40 μm and the detectors are realised by the formation of a nickel silicide on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the back side of 4H-SiC substrate. The low doping concentration (≅6×10 13 cm −3 ) of the epilayer allows the detector to be totally depleted at relatively low reverse voltages (≅100 V). We present experimental data on the charge collection properties by using 5.486 MeV α-particles impinging on the Schottky contact. A 100% charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the α-particle extrapolated range in SiC. The diffusion contribution of the minority change carriers to CCE is pointed out. By comparing measured CCE values to the outcomes of drift–diffusion simulation, values are inferred for the hole lifetime within the neutral region of the charge carrier generation layer

Mechanisms of Step-Stress Degradation In Carbon-Doped 0.15 μm AlGaN/GaN HEMTs for Power RF Applications

We discuss the degradation mechanisms of C-doped 0.15-μm gate AlGaN/GaN HEMTs tested by drain step-stress experiments. Experimental results show that these devices exhibit cumulative degradation effects during the step stress experiments in terms of either (i) transconductance (gm) decrease without any threshold-voltage (VT) change under OFF-state stress, or (ii) both VT and gm decrease under ON-state stress conditions. To aid the interpretation of the experiments, two-dimensional hydrodynamic device simulations were carried out. Based on obtained results, we attribute the gm decrease accumulating under OFF-state stress to hole emission from CN acceptor traps in the gate-drain access region of the buffer, resulting in an increase in the drain access resistance. On the other hand, under ON-state stress, channel hot electrons are suggested to be injected into the buffer under the gate and in the gate-drain region where they can be captured by CN traps, leading to VT and gm degradation, respectively

Epitaxial silicon carbide charge particle detectors

The 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

X-gamma Ray Spectroscopy With Semi-Insulating 4H-Silicon Carbide

Radiation detectors on a semi-insulating (SI) 4H silicon carbide (SiC) wafer have been manufactured and characterized with X and \u3b3 photons in the range 8-59 keV. The detectors were 400-\u3bcm-diameter circular Ni-SiC junctions on an SI 4H-SiC wafer thinned to 70 \u3bcm. Dark current densities of 3.5 nA/cm2 at +20\ub0C and 0.3 \u3bcA / cm2 at +104\ub0C with an internal electric field of 7 kV/cm have been measured. X-\u3b3 ray spectra from 241Am have been acquired at room temperature with pulser line width of 756 eV FWHM. The charge collection efficiency (CCE) has been measured under different experimental conditions with a maximum CCE = 75% at room temperature. Polarization effects have been observed, and the dependence of CCE on time and temperature has been measured and analyzed. The charge trapping has been described by the Hecht model with a maximum total mean drift length of 107 \u3bcm at room temperature

Experimental/numerical investigation of the physical mechanisms behind high-field degradation of power HFETs and their implications on device design

The mechanisms behind the high-field degradation of Al0.25Ga0.75/GaAs power heterojunction field effect transistors (HFET) were discussed. The surface trapping effects, such as gate lag, transconductance frequency dispersion, drain current kinks and their relationship with device degradation were analyzed. A hydrodynamic model was used to show that a combination of impact ionization and surface traps accounted for the kinks in the output curves and their post-stress enhancement

Influence of substrate on the performance of semi-insulating GaAs detectors

A 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

Reliability Investigation of GaN HEMTs for MMICs Applications

Results obtained during the evaluation of radio frequency (RF) reliability carried out on several devices fabricated with different epi-structure and field-plate geometries will be presented and discussed. Devices without a field-plate structure experienced a more severe degradation when compared to their counterparts while no significant correlation has been observed with respect of the different epi-structure tested. RF stress induced two main changes in the device electrical characteristics, i.e., an increase in drain current dispersion and a reduction in gate-leakage currents. Both of these phenomena can be explained by assuming a density increase of an acceptor trap located beneath the gate contact and in the device barrier layer. Numerical simulations carried out with the aim of supporting the proposed mechanism will also be presented

Surface-related kink effect in AlGaAs/GaAs power HFETs

We show that, differently from what generally accepted for GaAs- and InP-based HEMTs, where the kink is attributed to accumulation of impact-ionization-induced holes in the source access region [1,2], the kink arises in AlGaAs/GaAs HFETs from the combined effect of impact ionization and traps located at the gate-drain recess surface. Kink enhancement after hot-electron stress is a consequence of trap-density increase at this surface