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Gallium nitride (GaN) is a wide bandgap semiconductor material and is the most popular material after silicon in the semiconductor industry. The prime movers behind this trend are LEDs, microwave, and more recently, power electronics. New areas of research also include spintronics and nanoribbon transistors, which leverage some of the unique properties of GaN. GaN has electron mobility comparable with silicon, but with a bandgap that is three times larger, making it an excellent candidate for high-power applications and high-temperature operation. The ability to form thin-AlGaN/GaN heterostructures, which exhibit the 2-D electron gas phenomenon leads to high-electron mobility transistors, which exhibit high Johnson's figure of merit. Another interesting direction for GaN research, which is largely unexplored, is GaN-based micromechanical devices or GaN microelectromechanical systems (MEMS). To fully unlock the potential of GaN and realize new advanced all-GaN integrated circuits, it is essential to cointegrate passive devices (such as resonators and filters), sensors (such as temperature and gas sensors), and other more than Moore functional devices with GaN active electronics. Therefore, there is a growing interest in the use of GaN as a mechanical material. This paper reviews the electromechanical, thermal, acoustic, and piezoelectric properties of GaN, and describes the working principle of some of the reported high-performance GaN-based microelectromechanical components. It also provides an outlook for possible research directions in GaN MEMS.

This paper exhibits experimental and theoretical results on metamorphic high-electron mobility transistor (MM-HEMT). Modeling and measurements provide a better knowledge of device physics which allows us to optimize device structures. We present 10-GHz power performances, pulse and gate measurements, and two-dimensional (2-D) hydrodynamic modeling of enhancement-mode (E-mode) Al/sub 0.66/In/sub 0.34/As/Ga/sub 0.67/In/sub 0.33/As NM-HEMT devices. It is the first time that cap layer thickness has been studied for a MM-HEMT. A typical reverse breakdown voltage of 16 V has been obtained. Gate current issued from impact ionization has been shown, for the first time, in such a device. The 2-D hydrodynamic model is a useful tool for cost engineering because it brings more information in terms of physical quantity distributions, necessary to predict breakdown behavior of FET. The 10-GHz measurements with a load-pull power set-up demonstrate the capabilities for a thick cap device with large gate-to-drain extension since an output power of 140 mW/mm have been obtained which is the state-of-the-art for such a device. These results obtained confirm the great interest of the structures for power application systems. The only work reported, to our knowledge, using a MM-HEMT structure in E-mode with an indium content close to 50% has been studied by Eisenbeiser et al.. Their typical gate-to-drain breakdown voltage was 5.2 V. The 0.6 /spl mu/m /spl times/3 mm devices exhibited 30 mW/mm at 850 MHz.

FET's with double stepped gate recess are commonly admitted to be presently a very convenient structure capable to overcome the fundamental power limitation related to the breakdown voltage. The present paper deals with an analysis of a double recessed MESFET with a very good and instructive breakdown performance. For the first time we explain on the basis of gate current observations why the double recess structure allows a large breakdown improvement not only at pinch off voltage but also at open channel. Moreover it is shown that the breakdown optimization is fully compatible with the microwave gain performance. >

We report on a double-pulse doped, double recess In/sub 0.35/Al/sub 0.65/As-In/sub 0.35/Ga/sub 0.65/As metamorphic high electron mobility transistor (MHEMT) on GaAs substrate. This 0.15-/spl mu/m gate MHEMT exhibits excellent de characteristics, high current density of 750 mA/mm, extrinsic transconductance of 700 mS/mm. The on and off state breakdown are respectively of 5 and 13 V and defined It gate current density of 1 mA/mm. Power measurements at 60 GHz were performed on these devices. Biased between 2 and 5 V, they demonstrated a maximum output power of 390 mW/mm at 3.1 V of drain voltage with 2.8 dB power gain and a power added efficiency (PAE) of 18%. The output power at 1 dB gain compression is still of 300 mW/mm. Moreover, the linear power gain is of 5.2 dB. This is to our knowledge the best output power density of any MHEMT reported at this frequency.

It is pointed out that among the large variety of heterostructure field effect transistors, multichannel devices present a particular originality: their transconductance profile is very flexible and depends on the structure parameters. They are therefore suited for high signal nonlinear applications. The specific case of double quantum-well structures is studied. Conventional and pseudomorphic devices are characterized under DC and RF conditions. Very high current densities (up to 1.2 A/mm) are demonstrated. The effect of different structural parameters on the transconductance and cutoff frequency is discussed. The results are analyzed in order to give a full understanding of these devices and to demonstrate their performances. >

Current dispersion effects have been experimentally investigated in a variety of AlGaN/GaN heterostructure FETs with large signal and switching measurements including HEMTs with doped and undoped barrier layer. A range of dispersion frequencies from 10/sup -3/ Hz to 10 GHz were observed, where the output current amplitude is drastically reduced. Through this effect the full channel charge of an AlGaN/GaN heterostructure FET may be completely depleted under specific bias conditions. This indicates that this phenomena cannot be related to deep traps alone, but is also connected to piezorelated charge states and conduction to these states.

This paper presents original and experimental results provided by E-mode Al/sub 0.67/In/sub 0.33/As/Ga/sub 0.66/In/sub 0.34/As metamorphic HEMT. The devices exhibit good dc and rf performances. The 0.4 /spl mu/m gate length devices have saturation current density of 355 mA/mm at +0.6 V gate-to-source voltage. The Schottky characteristic is a typical reverse gate-to-drain breakdown voltage of -16 V. It is the first time, to our knowledge, that gate current issued from impact ionization have been observed in these devices versus gate to drain extension. These results are the first reported for E-mode Al/sub 0.67/In/sub 0.33/As/Ga/sub 0.66/In/sub 0.34/As MM-HEMTs on GaAs substrate.

A 0.1-/spl mu/m T-gate pseudomorphic Ga/sub 0.51/In/sub 0.49/P/In/sub 0.2/Ga/sub 0.8/As/GaAs high electron mobility transistor (PM-HEMT) has been successfully developed on GaAs substrate. Each technological step has been optimized as the growth by gas source molecular beam epitaxy (GSMBE), the ohmic contacts, and the gate recess for high-frequency applications. This device with a single /spl delta/ doping exhibits excellent dc and radio frequency (RF) performances with a current density of 700 mA/mm in combination with a high breakdown voltage of 9 V, an extrinsic transconductance Gm higher than 700 mS/mm, and a current gain cutoff frequency Ft of 120 GHz at V/sub ds/=2 V. Power measurements at 60 GHz have been performed on these devices. They have demonstrated a maximum output power density of 560 mW/mm with 4.6-dB power gain and a power-added efficiency (PAE) of 22.5%, These are the first power results at V-band ever reported for GaInP/InGaAs/GaAs pseudomorphic HEMTs.

An In/sub 0.3/Al/sub 0.7/As/In/sub 0.3/Ga/sub 0.7/As metamorphic power high electron mobility transistor (HEMT) grown on GaAs has been developed. This structure with 30% indium content presents several advantages over P-HEMT on GaAs and LM-HEMT on InP. A 0.15-/spl mu/m gate length device with a single /spl delta/ doping exhibits a state-of-the-art current gain cut-off frequency F/sub t/ value of 125 GHz at V/sub ds/=1.5 V, an extrinsic transconductance of 650 mS/mm and a current density of 750 mA/mm associated to a high breakdown voltage of -13 V, power measurements performed at 60 GHz demonstrate a maximum output power of 240 mW/mm with 6.4-dB power gain and a power added efficiency (PAE) of 25%. These are the first power results ever reported for any metamorphic HEMT.

In this work we report on the state-of-the-art combination at V-band between simultaneously power density (370 mW/mm), power-added efficiency (28.3%), and power gain (5.2 dB) of InP pseudomorphic HEMTs biased at a low drain voltage of 2 V. The performance of these double delta-doped pseudomorphic AlInAs-GaInAs HEMTs on InP with an original strain compensated channel was measured at 60 GHz. This demonstrates a good potentiality for low-voltage applications in order to reduce the power supply of systems.

This paper reports the study of an HEMT, the characteristic of which is to have a decoupling capacitor directly integrated between its drain and source electrodes. It is shown that, with an appropriate design of this basic filtering element, such a device proves to be efficient as for the realization of hybrid gate mixers. An experimental demonstration of this property is given by comparing a HEMT without capacitor with a HEMT with an integrated capacitor. For the latter, the gate length of which is 0.3 /spl mu/m, it is shown that, at 18 GHz, a 5-dB improvement of conversion gain is provided by the integrated capacitor. >

This paper provides an analysis of the power performance degradations of interdigitated HEMTs in millimeter wave range as the total gate width increases. It investigates the possibility of optimizing the device topology by combining a limited number of via holes and airbridge source connections in order to offer a good cost-performance trade off. >

This paper examines the problem of modeling HEMT's for calculations of conversion gain and intermodulation. An accurate and simple large signal model of discrete HEMT's has been developed. The nonlinear elements of the model are assumed to depend exclusively on the gate-source voltage. The interpolation of the measured data, using polynomial expressions, provides a description of the HEMT's nonlinearities in a CAD software. Based on the model, a hybrid HEMT gate mixer has been built. The accuracy of the model has been verified, and we obtained good agreement between the measured and simulated results. >

This paper presents the realization and simulation of a new subharmonic gate mixer based on a multichannel HEMT. This device gives the possibility of tailoring the transconductance profile. Two peaks separated by a valley can be obtained. Biasing the device at the bottom of the valley. the IF signal comes from the mixing of the RF signal and the second LO harmonic. This mixer uses half the normal LO frequency and has a minimum conversion loss of 10 dB. >

A metal-semiconductor-metal detector with a InGaAs/GaAs superlattice active layer showing efficient photoresponse up to 1.35 mu m is discussed. The active layer with an In composition of approximately 64% is grown by molecular beam epitaxy on a GaAs substrate at 460 degrees C. The large size detector (200*200 mu m/sup 2/) shows bias-dependent DC gain, fast response speed (FWHM >