Malek Zegaoui

Effects of AlGaN Back Barrier on AlN/GaN-on-Silicon High-Electron-Mobility Transistors

In this work, the effects of an AlGaN back barrier in the dc and RF performances of AlN/GaN high-electron-mobility transistors (HEMTs) grown on 100 mm Si substrates have been investigated. It is shown that the outstanding dc performance in highly scaled AlN/GaN-on-Si HEMTs can be fully preserved when introducing an AlGaN back barrier while significantly reducing the sub-threshold drain leakage current and enhancing the RF performance by the reduction of short-channel effects. Therefore, the AlN/GaN/AlGaN double heterostructure enables high-aspect-ratio devices generating extremely high current density, low leakage current, and high voltage operation.

Above 600 mS/mm Transconductance with 2.3 A/mm Drain Current Density AlN/GaN High-Electron-Mobility Transistors Grown on Silicon

AlN/GaN high-electron-mobility transistors (HEMTs) capped with an in-situ grown SiN have been successfully developed on 100 mm Si substrates. A unique combination of maximum output current density exceeding 2 A/mm and a record extrinsic transconductance above 600 mS/mm has been reached, which is well beyond the highest reported values of any GaN-on-Si HEMTs. The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 85 and 103 GHz with 0.16-?m gate length, respectively, resulting in a high fT?Lg product that promises low-cost, high performance millimeter wave electronics.

Energy-Autonomous Picocell Remote Antenna Unit for Radio-Over-Fiber System Using the Multiservices Concept

The study reported in this letter deals with the extension of the multiservices concept to radio-over-fiber systems with energy-autonomous picocell remote antenna units. Continuous-power, radio-frequency, and digital signals have been combined in a single multimode fiber for the first time. The results clearly demonstrate no impairment of the optically powered remote antenna unit compared to an electrically powered version. The proposed system complies with the classical baseband Ethernet high-data-rate network (10 GbE bit error rate 10-12). The measured error vector magnitude for the radio-frequency (IEEE802.11g) signal transmission through the designed system stays around 2%, including both the optical transmission over 100-m OM3 multimode fiber and a wireless coverage of 5 m.

High electron mobility in high-polarization sub-10 nm barrier thickness InAlGaN/GaN heterostructure

We report on the improvement of the electron transport properties of the two-dimensional electron gas (2DEG) confined at a nearly lattice-matched quaternary barrier InAlGaN/AlN/GaN heterostructure using a sub-10 nm ultrathin barrier. Electron mobilities of 1800 (RT) and 6800 cm2 V−1 s−1 (77 K) are achieved while delivering a high electron density of 1.9 × 1013 cm−2, resulting in extremely low sheet resistances of 191 Ω/ at RT and below 50 Ω/ at 77 K. These 2DEG properties exceed the best ones ever reported for III–N structures. The excellent current and power gain cut-off frequencies of 60 and 190 GHz at VDS = 15 V obtained using 0.25 µm technology reflect the outstanding 2DEG properties.

1.55-

We report a GaNAsSb-based photoconductive switch for microwave switching application. The GaNAsSb layer was grown by molecular beam epitaxy in conjunction with a radio-frequency plasma-assisted nitrogen source and a valved antimony cracker cell. The switch shows a maximum ON-OFF ratio of 9 dB at 1.5 GHz under 1.55-m laser excitation at 80 mW. The switch also shows a positive ON-OFF ratio up to 10 GHz. This is the first successful demonstration of a photoconductive switch for microwave switching application under 1.55- m wavelength excitation. Further analysis suggests that the high contact resistance may degrade the performance of the photoconductive switch.

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This letter demonstrates an original carrier-induced effects InP digital optical switch (DOS) designed to achieve a low optical crosstalk for 1.55-mum wavelength applications. It is based on a widened multimode Y-junction combined with a sinusoidal shape waveguide to increase the optical contrast ratio between the two output branches. The entire InP-InGaAsP-InP DOS was designed using a semi-vectorial three-dimensional beam propagation method. The fabricated InP DOS with lambdag = 1.3 mum heterostructure exhibits an optical crosstalk as low as -38.5 dB for a 33-mA switching current at 1.55-mum wavelength for a favourable polarized input light.

m GaNAsSb-Based Photoconductive Switch for Microwave Switching

CuInS2 thin films were prepared via the sol–gel process. X-ray diffraction (XRD) studies reveal that the thin films are well crystallized and they crystallize in a chalcopyrite phase. Hall-effect measurements were carried out, for the first time, on chalcopyrite CuInS2 films elaborated by the sol–gel method. Hence, the resistivity of the p-type CuInS2 films was found to be around 40 Ωcm and the carrier density was in the 1016 cm-3 range. Furthermore, the UV–vis absorption spectra show that the energy bandgap is 1.47 eV, a value close to the most favorable bandgap (1.53 eV) for solar cells.

A New Low Crosstalk InP Digital Optical Switch Based on Carrier-Induced Effects for 1.55-

This paper reviews the recent progress in GaNAsSb material for photonic and electronic applications. All the results and data presented in this review article are summarized from our previously published works in refs. 6-12. Photoresponsivity of 12A/W and cut-off frequency of 4.5GHz were achieved in the 1.3µm GaNAsSb based photodetector. A GaNAsSb/GaAs optical waveguide system was also demonstrated at 1.55µm. The GaNAsSb based photoconductive switch exhibits pulsed response with FWHM of 30ps and photoresponse of up to 1.6µm. The turn-on voltage of the device fabricated from GaNAsSb based HBT is ~330mV lower than that of a conventional AlGaAs/GaAs HBT.

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The aim of this work is to present a potential application of gallium nitride-based optoelectronic devices. By using a laser diode and a photodetector, we designed and demonstrated a free-space compact and lightweight wireless power transfer system, whose efficiency is limited by the efficiency of the receiver. We analyzed the effect of the electrical load, temperature, partial absorption and optical excitation distribution on the efficiency, by identifying heating and band-filling as the most impactful processes. By comparing the final demonstrator with a commercial RF-based Qi system, we conclude that the efficiency is still low at close range, but is promising in medium to long range applications. Efficiency may not be a limiting factor, since this concept can enable entirely new possibilities and designs, especially relevant for space applications.

m Applications

We report on extremely low off-state leakage current in AlGaN/GaN-on-silicon metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) up to a high blocking voltage. Remarkably low off-state gate and drain leakage currents below 1 µA/mm up to 3 kV have been achieved owing to the use of a thick in situ SiN gate dielectric under the gate, and a local Si substrate removal technique combined with a cost effective 15-µm-thick AlN dielectric layer followed by a Cu deposition. This result establishes a manufacturable state-of-the-art high-voltage GaN-on-silicon power transistors while maintaining a low specific on-resistance of approximately 10 mΩcm2.