A comprehensive model for the electron mobility in wurtzite (hexagonal) GaN is developed. A large number of experimental mobility data and the results of Monte Carlo transport simulations reported in the literature have been evaluated and serve as the basis for the model development. The proposed model describes the dependence of the mobility on carrier concentration, temperature, and electric field. Good agreement between the modeled low-field mobility and measured data at both room and elevated temperatures has been obtained. The Monte Carlo results of the high-field transport are correctly reproduced by the model. The model can be easily incorporated into numerical device simulators.

An electron mobility model for wurtzite GaN

This paper presents a nonlinear equivalent circuit model of microwave power GaN high electron-mobility transistors (HEMTs), amenable for integration into commercial harmonic balance or transient simulators. All the steps taken to extract its parameter set are explained, from the extrinsic linear elements up to the intrinsic nonlinear ones. The predictive model capabilities are illustrated with measured and simulated output power and intermodulation-distortion data of a GaN HEMT. The model is then fully validated in a real application environment by comparing experimental and simulated results of output power, power-added efficiency, and nonlinear distortion obtained from a power amplifier.

http://www.av.it.pt/nbcarvalho/docs/Revista19.pdf

Nonlinear device model of microwave power GaN HEMTs for high power-amplifier design

The performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on diamond and SiC substrates is examined. We demonstrate GaN-on-diamond transistors with periphery WG = 250 mum, exhibiting ft = 27.4 GHz and yielding a power density of 2.79 W/mm at 10 GHz. Additionally, the temperature rise in similar devices on diamond and SiC substrates is reported. To the best of our knowledge, these represent the highest frequency of operation and first-reported thermal and X -band power measurements of GaN-on-diamond HEMTs.

Comparison of GaN HEMTs on Diamond and SiC Substrates

We report on the development of time-resolved Raman thermography to measure transient temperatures in semiconductor devices with submicrometer spatial resolution. This new technique is illustrated for AlGaN/GaN HFETs and ungated devices grown on SiC and sapphire substrates. A temporal resolution of 200 ns is demonstrated. Temperature changes rapidly within sub-200 ns after switching the devices on or off, followed by a slower change in device temperature with a time constant of ~10 and ~140 mus for AlGaN/GaN devices grown on SiC and sapphire substrates, respectively. Heat diffusion into the device substrate is also demonstrated

Time-Resolved Temperature Measurement of AlGaN/GaN Electronic Devices Using Micro-Raman Spectroscopy

This paper presents a comprehensive review of AlGaN/GaN high electron mobility transistor failure physics and reliability, focusing on mechanisms affecting the gate-drain edge, where maximum electric field and peak temperatures are reached. Physical effects at the origin of device degradation (inverse piezoelectric effect, time-dependent trap formation and percolative conductive paths formation, and electrochemical AlGaN and GaN degradation) are discussed on the basis of literature data and unpublished results. Thermally activated mechanisms involving metal-metal and metal-semiconductor interdiffusion at the gate Schottky junction are also discussed.

AlGaN/GaN-Based HEMTs Failure Physics and Reliability: Mechanisms Affecting Gate Edge and Schottky Junction

Amplifiers for a next generation of T/R-modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the bases of novel AlGaN/GaN HEMT structures. Both, low noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high power amplifier (HPA) are measured. The measured noise figure of the low noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multilayer LTCC technology.

GaN MMIC based T/R-Module Front-End for X-Band Applications

A state-space approach to large-signal (LS) modeling of high-speed transistors is presented and used as a general framework for various model descriptions of the dispersive features frequently observed for HEMTs at low frequency. Ensuring unrestricted LS-small-signal (SS) model compatibility, the approach allows to construct LS models from multibias SS S-parameter measurements. A general transformation between state-space models is derived, which are equivalent in the SS limit, but nonequivalent under LS stimuli. This transformation has the potential to compensate deviations observed by comparing model predictions with LS measurements and to find an optimum state linear LS model without any change of the SS behavior

A Systematic State–Space Approach to Large-Signal Transistor Modeling

This work presents a two-stage high-power amplifier monolithic microwave integrated circuit (MMIC) operating between 9 GHz and 11 GHz based on a fully integrated AlGaN/GaN high electron mobility transistor (HEMT) technology on s.i. SiC substrate and is suitable for radar applications. The MMIC device with a chip size of 4.5/spl times/3 mm/sup 2/ yields a linear gain of 20 dB and a maximum pulsed saturated output power of 13.4 W at 10 GHz equivalent to 3.3 W/mm at V/sub DS/=35V, 10% duty cycle, and a gain compression level of 5 dB. Further, dc reliability data are given for the MMIC HEMT technology.

A coplanar X-band AlGaN/GaN power amplifier MMIC on s.i. SiC substrate

We report on recent results from our GaN transistor and circuit technology. Epitaxial growth can be performed on either SiC or Si substrates in order to provide high-quality AlGaN/GaN heterostructures. These heterostructures are then utilized in order to realize transistors and integrated circuits ranging from high-voltage transistors for voltage conversion in efficient power switches, L/S-band power bars and X-band MMICs for next-generation communication systems, and finally W-band MMICs for radar applications. The technology is characterized by state-of-the-art performance, good uniformity and high yield as well as excellent long-term stability. In combination with the space compatibility we believe that this technology is ideal for space. X-band MMICs from Fraunhofer IAF are scheduled to have the first in-orbit demonstration of European GaN within the Proba-V mission which is planned to be launched in spring 2013.

https://iopscience.iop.org/article/10.1088/0268-1242/28/7/074010/pdf

GaN HEMTs and MMICs for space applications

We present a systematic study of epitaxial growth, processing technology, device performance and reliability of our GaN HEMTs and MMICs manufactured on 3 inch SiC substrates. Epitaxy and processing are optimized for both performance and reliability. The deposition of the AlGaN/GaN HEMT epitaxial structures is designed for low background carrier concentration and a low trap density in order to simultaneously achieve a high buffer isolation and low DC to RF dispersion. Device fabrication is performed using standard processing techniques involving both electron-beam and stepper lithography. Gate lengths of 250 nm and 500 nm are employed for 10 GHz and 2 GHz applications, respectively. The developed HEMTs demonstrate excellent high-voltage stability, high power performance and large power added efficiencies. Devices exhibit two-terminal gate―drain breakdown voltages in excess of 160 V (current criterion 1 mA/mm) across the entire 3 inch wafer with parasitic gate and drain currents well below 1 mA/mm when biased up to 80 V drain bias under pinch-off conditions. Load-Pull measurements at 2 GHz on 800 μm gate width devices return a well-behaved relationship between bias-voltage and output-power as well as power-added- efficiencies beyond 60% up to U DS = 100 V. For a drain bias of 100 V an output-power-density around 22 W/mm with 26 dB linear gain is obtained. On large devices (32 mm gate width packaged in industry-standard ceramic packages) an output power beyond 100 W is achieved with a PAE above 50% and a linear gain around 15 dB. Dual-stage MMICs in microstrip transmission line technology yield a power added efficiency of 40% at 8.56 GHz for a power level of 11 W. A single-stage MMIC yields a PAE of 46% with 7 W of output power at V DS = 28 V. Reliability is tested on HEMT devices having a gate periphery of 8 x 60 μm at an operating bias of 50 V under both DC and RF conditions. About 10% drain-current change under DC-stress (50 mA/mm) is observed af- ter more than 1000 h of operation with an extrapolated drain- current degradation below 20% after 200000 h (more than 20 years) of operation. Under RF stress (2 GHz, 1 dB compression) the observed change in output power density is be- low 0.2 dB after more than 1000 h.

F. van Raay

Papers

GaN MMIC based T/R-Module Front-End for X-Band Applications

A Systematic State–Space Approach to Large-Signal Transistor Modeling

A coplanar X-band AlGaN/GaN power amplifier MMIC on s.i. SiC substrate

GaN HEMTs and MMICs for space applications

GaN HEMT and MMIC development at Fraunhofer IAF: performance and reliability