M. Rousseau

Effects of Self-Heating on Performance Degradation in AlGaN/GaN-Based Devices

A self-consistent electrothermal transport model that couples electrical and thermal transport equations is established and applied to AlGaN/GaN device structures grown on the following three different substrate materials: 1) SiC; 2) Si; and 3) sapphire. Both the resultant I-V characteristics and surface temperatures are compared to experimental I -V measurements and Raman spectroscopy temperature measurements. The very consistent agreement between measurements and simulations confirms the validity of the model and its numerical rendition. The results explain why the current saturation in measured I-V characteristics occurs at a much lower electric field than that for the saturation of electron drift velocity. The marked difference in saturated current levels for AlGaN/GaN structures on SiC, Si, and sapphire substrates is directly related to the different self-heating levels that resulted from the different biasing conditions and the distinctive substrate materials.

Power Performance of AlGaN/GaN High-Electron-Mobility Transistors on (110) Silicon Substrate at 40 GHz

This letter reports the first millimeter-wave power demonstration of AlGaN/GaN high-electron-mobility transistors grown on a (110) silicon substrate. Owing to an AlN/AlGaN stress-mitigating stack and in spite of the twofold surface symmetry of Si (110), it is possible to obtain crack-free GaN layers for the fabrication of millimeter-wave power devices with high performance. The device exhibits a maximum dc drain current density of 1.55 A/mm at VGS = 0 V with an extrinsic transconductance of 476 mS/mm. An extrinsic current gain cutoff frequency of 81 GHz and a maximum oscillation frequency of 106 GHz are deduced from Sij parameters. At 40 GHz, an output power density of 3.3 W/mm associated with a power-added efficiency of 20.1% and a linear power gain of 10.6 dB is obtained.

Enhancement-mode Al/sub 0.66/In/sub 0.34/As/Ga/sub 0.67/In/sub 0.33/As metamorphic HEMT, modeling and measurements

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.

Analysis of Thermal Effect Influence in Gallium-Nitride-Based TLM Structures by Means of a Transport–Thermal Modeling

The power dissipation in a semiconductor device usually generates a self-heating effect, which becomes very significant for gallium nitride power applications. The operating temperature of these devices increases significantly, and the transport properties are then degraded (IEEE Electron Device Lett., vol. 24, p. 375, 2003; IEEE Electron Device Lett., vol. 49, p. 1496, 2002; IEEE Trans. Electron Devices, vol. 52, p. 1683, 2005). Taking heating effects into account explains the physical phenomena observed in experiments, due in particular to the fact that temperature greatly affects the velocity. In this paper, numerical simulations are carried out to study the influence of thermal effects on the static characteristics of GaN transmission line measurement (TLM) model structures. A transport-thermal model is thus developed in order to take into account both the electrical and the thermal phenomena in a coupled way. This paper uses GaN TLMs on sapphire substrates. Simulations have shown that the saturation current is reached for electric fields much lower than the saturation electric field, thus confirming the experimental results

AlGaN/GaN HEMT High Power Densities on

In this letter, successful operation at 10 GHz of T-gate HEMTs on epitaxial structures grown by metal-organic chemical vapor deposition (MOCVD) or MBE on composite substrates is demonstrated. The used device fabrication process is very similar to the process used on monocrystalline SiC substrate. High power density was measured on both epimaterials at 10 GHz. The best value is an output power density of 5.06 W/mm associated to a power-added efficiency (PAE) of 34.7% and a linear gain of 11.8 dB at VDS = 30 V for the components based on MOCVD-grown material. The output power density is 3.58 W/mm with a maximum PAE of 25% and a linear gain around 15 dB at VDS = 40 V for the MBE-grown material.

\hbox{SiC/} \hbox{SiO}_{2}

This letter describes the thermal behavior of AlGaN/GaN high electron mobility transistors on different substrates thanks to a fully consistent physical-thermal model. Self-heating explains the drastic reduction in the current flowing from drain to source. It is shown that, in order to keep the material from significantly degrading at the gate exit, the maximum dissipated power must be limited to 7 W/mm, 13 W/mm, and 38 W/mm for silicon, silicon carbide, and diamond substrates, respectively. These results have been validated from experimental thermal measurements.

/poly-SiC Substrates

Abstract A two dimensional-hydrodynamic model is carried out to predict the performance of short gate length power field effect transistors based on III–V semi-conductor systems. The model is based on the conservation equations, deduced from the Boltzmann transport equation, solved in their whole form by taking temporal and spatial variations in carrier momentum into account. This model is well suited to get accurate predictions for power devices having various gate recess topologies. Results are performed for devices with different gate lengths and compared with those obtained from simplified models. For gate lengths shorter than 0.5 μm, a drop in the overshoot velocity phenomenon involves a better estimation of the characteristics of the device.

Efficient physical-thermal model for thermal effects in AlGaN/GaN high electron mobility transistors

Optical waveguiding properties of a thick wurtzite aluminum nitride highly [002]-textured hetero-epitaxial film on (001) basal plane of sapphire substrate are studied. The physical properties of the film are determined by X-ray diffraction, atomic force microscopy, microRaman, and photocurrent spectroscopy. The refractive index and the thermo-optic coefficients are determined by m-lines spectroscopy using the classical prism coupling technique. The optical losses of this planar waveguide are also measured in the spectral range of 450-1553u2009nm. The lower value of optical losses is equal to 0.7 dB/cm at 1553u2009nm. The optical losses due to the surface scattering are simulated showing that the contribution is the most significant at near infrared wavelength range, whereas the optical losses are due to volume scattering and material absorption in the visible range. The good physical properties and the low optical losses obtained from this planar waveguide are encouraging to achieve a wide bandgap optical guiding platform from these aluminum nitride thin films.

Two-dimensional hydrodynamic model including inertia effects in carrier momentum for power millimetre-wave semi-conductor devices

The design of power GaN devices has to take into account the impact of temperature on device materials due to highly dissipated power and a consequent large self-heating. The accurate knowledge of transport properties as a function of the lattice temperature is essential in order to make a good thermal management to optimise the device performance. In this paper, accurate expressions describing the main transport properties as function of temperature and electric field for wurtzite GaN have been extracted starting from Monte Carlo simulations and then using a genetic algorithm. In particular, these expressions take into account the abrupt change in electron velocity slope at a low electric field (~20 kV/cm). Using the same methodology, we have determined the temperature dependence of other physical parameters such as the low field mobility, saturation velocity, critical electric field and the corresponding peak velocity in a temperature range of 300 K – 700 K. The results show a very good agreement between the theoretical and experimental values.

Dispersion properties and low infrared optical losses in epitaxial AlN on sapphire substrate in the visible and infrared range

This paper shows the capability of AlGaN/GaN high electron mobility transistors (HEMTs) on (001) oriented silicon substrate with 300 nm gate length using unstuck Gamma gate for low cost device microwave power applications. The total gate periphery of 300 mum, exhibits a maximum DC drain current density of 600 mA/mm at VDS=7V with an extrinsic transconductance (gm max) around 200 mS/mm. An extrinsic current gain cutoff frequency (fT) of 37 GHz and a maximum oscillation frequency (fmax) of 55 GHz are deduced from Sij-parameters measurements. At 10 GHz, an output power density of 2.9 W/mm associated to a power added efficiency (PAE) of 20% and a linear gain of 7 dB are obtained at VDS=30 V and VGS=-2 V.