M. Zegaoui

First Demonstration of High-Power GaN-on-Silicon Transistors at 40 GHz

In this letter, high-output-power-density GaN-based high-electron-mobility transistors grown on a 100-mm silicon substrate is demonstrated for the first time at 40 GHz. The use of an optimized double heterostructure based on ultrathin barrier AlN/GaN allows both high current density and low leakage current, resulting in high-frequency performance (fmax close to 200 GHz). Furthermore, the control of the trapping effects on these highly scaled devices enabled to set a first benchmark at 40 GHz with 2.5 W/mm at VDS = 15 V, mainly limited by RF losses and thermal issues. These results show that an AlN/GaN/AlGaN heterostructure grown on silicon substrate is a viable technology for cost-effective high-power millimeter-wave amplifiers fully compatible with standard Si-based devices.

High-Performance Low-Leakage-Current AlN/GaN HEMTs Grown on Silicon Substrate

In this letter, ultrathin-barrier AlN/GaN high-electron mobility transistors (HEMTs) capped with in situ metal-organic-chemical-vapor-deposition-grown SiN have been successfully fabricated on 100-mm Si substrates. Output current density exceeding 2 A/mm has been reached, which represents, to the best of our knowledge, the highest value ever achieved for GaN-on-Si HEMTs. This results from the high 2DEG density of the optimized AlN/GaN heterostructure. Despite the ultrathin barrier of 6 nm, low gate and drain leakage currents of about 10 μA/mm are obtained without the use of a gate dielectric that generally induces reliability issues. Furthermore, the high aspect ratio (gate length Lg/gate-to-channel distance) and low RF losses (at the buffer/Si substrate interface) are reflected in excellent RF performances. The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 52 and 102 GHz with a 0.2- μm gate length, respectively, resulting in an fT·Lg product as high as the reported state-of-the-art GaN-on-Si HEMTs.

Demonstration of low leakage current and high polarization in ultrathin AlN/GaN high electron mobility transistors grown on silicon substrate

High quality AlN/GaN heterostructures grown on silicon substrate are demonstrated. It is found that high carrier concentration can be achieved whereas circular diodes showed a low leakage current up to 200 V reverse bias. 200 nm gate length AlN/GaN transistors exhibited a drain current density of 1.3 A/mm with a pinchoff leakage current below 20 μA/mm and a record GaN-on-silicon extrinsic transconductance of 470 mS/mm. These results demonstrate the possibility to achieve a unique combination of large polarization with a barrier thickness as low as 3 nm while preserving a remarkably low device leakage current without using any gate insulator.

Low-Noise Microwave Performance of AlN/GaN HEMTs Grown on Silicon Substrate

Microwave noise performance of state-of-the-art AIN/GaN high-electron-mobility transistors (HEMTs) grown on 100-mm Si substrate has been investigated. DC and RF measurements show the outstanding potential of this structure for high power millimeter-wave (mmW) applications. A maximum output current density of about 2 A/mm, together with a low gate leakage current, and a record GaN-on-Si extrinsic transconductance above 600 mS/mm are demonstrated. The current gain cutoff frequency fT and the maximum oscillation frequency fmax were 85 and 103 GHz, respectively, with a 0.16-μm gate length. At VDS = 4 V, the device exhibits a minimum noise figure (NFmin) of 1 dB (1.8 dB) with an associated gain (GA) of 12 dB (10 dB) at 10 GHz (18 GHz) favorably comparable to the best reported GaN-on-Si HEMTs. These results show that AIN/GaN HEMTs grown on silicon substrate are promising for the integration of cost effective, low noise, and high power mmW amplifiers.

Sub-1-dB Minimum-Noise-Figure Performance of GaN-on-Si Transistors Up to 40 GHz

We report on the millimeter-wave noise performance of AlN/GaN/AlGaN double heterostructure (DHFET) grown on a 100-mm Si substrate with low-noise properties up to 40 GHz. The ultrathin-barrier GaN DHFETs simultaneously exhibit high current density, high transconductance, and high frequency performance (above 100 GHz) while showing low dc-to-RF dispersion and low gate and drain leakage currents. Consequently, sub-1-dB minimum noise figure at 36 GHz with an associated gain of 7.5 dB has been achieved. To our knowledge, this is the best noise performance reported in the Ka-band for any GaN device.

Optical devices for ultra-compact photonic integrated circuits based on III-V/polymer nanowires

We demonstrated the potential application of III-V/polymer nanowires for photonic integrated circuits in a previous paper. Hereby, we report the use of a spot size converter based on 2D reverse nanotaper structure in order to improve the coupling efficiency between the nanowire and optical fiber. A total coupling enhancement of up to a factor 60 has been measured from an 80 nm x 300 nm cross-section tip which feeds an 300 nm-side square nanowire at its both ends. Simultaneously, micro-radius bends have been fabricated to increase the circuit density; for a radius of 5 microm, the 90 masculine bend losses were measured as low as 0.60 dB and 0.80 dB for TE and TM polarizations respectively.

Optical Nanowires for Microwave Applications

In this paper, we propose to take advantage of specific properties of nanophotonics to achieve microwave functions which are difficult to get with more conventional ways. With this goal, we developed new technologies to fabricate III-V nanowaveguides. Two ways were explored: the first one by deep etching of conventional epitaxies and the second one by embedding nanowires in polymer. We show in this paper some results on first devices mainly based on nanowires embedded in polymer.

Recent developments in amorphous sputterred ITO thin films acting as transparent front contact layer of CIGS solar cells for energy autonomous wireless microsystems

In this paper, we report on the study of electrical, optical and structural properties of RF sputtered Indium Tin Oxide (ITO) thin films at room temperature. These films are dedicated to act as front electrode of CIGS solar microcells and shall so compel with the electrical and optical criteria that are required for such an application. It is well-known that the main drawback of the sputtering deposition technique deals with the inherent generation of highly energetic particles that causes bombardment onto the sample. The developed deposition process targets to be damage free onto the underlying layer since, in the case of CIGS solar cells, it is crucial to preserve the surface and the properties of the absorber layer on which these films will be deposited. At room temperature, it can be considered that amorphous ITO films are only obtained when this energetic bombardment does not occur. This can be obtained if the kinetic energy of the particles is fully dissipated by collisions within the deposition plasma [1–3]. The deposition process is developed in a conventional magnetron sputtering system without external heating, in such a way that films shall be amorphous. Furthermore, film internal stress is kept very low. Optical studies show a transparency over 80% in the visible range and a high transparency in the infrared region. The lowest obtained sheet resistance is 12.6 Ω/□ (∼ 300nm film thickness) with a carrier concentration of 2.4 × 1020 cm−3 and a carrier mobility of 45.1 cm2/V.s. As we can deposit a dual ITO layer structure, with a different resistivity level being attributed to each layer, we suggest our amorphous ITO thin films can be deposited directly above the absorbing CIGS material to act as both highly resistive (HR) and electrode layer.

Design, optimization and fabrication of an optical mode filter for integrated optics

We present the design, optimization, fabrication and characterization of an optical mode filter, which attenuates the snaking behavior of light caused by a lateral misalignment of the input optical fiber relative to an optical circuit. The mode filter is realized as a bottleneck section inserted in an optical waveguide in front of a branching element. It is designed with Bézier curves. Its effect, which depends on the optical state of polarization, is experimentally demonstrated by investigating the equilibrium of an optical splitter, which is greatly improved however only in TM mode. The measured optical losses induced by the filter are 0.28 dB.

InP Digital Optical Switch with 40dB crosstalk at 1.55μm wavelength

A New InP Digital Optical Switch especially designed for high crosstalks is proposed. More than 40dB crosstalk can be achieved at 1.55μm wavelength for switching current ranging from 35 to 90mA, depending on the optical polarisation.