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This paper reports the impact of epi-layer quality on the short-term reliability of GaN/AlGaN/GaN heterostructure field-effect transistors fabricated on Si substrates. At an early stage of 50 V high-temperature operating life tests, they exhibited a significant lowering of the forward breakdown voltage. The mean time to failure (MTTF) determined by this degradation mode was exponentially increased by decreasing full-width at half-maximum (FWHM) values of X-ray rocking curves. In small FWHM samples, extrapolated MTTF values exceeded 1\times 10^7~h at Tch=150^\circ\rm C. Alternatively, another degradation mode such as drain current degradation will dominate the long-term reliability at this temperature range. High-resolution transmission electron microscope and energy dispersive X-ray spectroscopy analyses revealed thinning or partial vanishment of GaN cap layer in a degraded sample. Gate current–voltage characteristics calculation based on the self-consistent Schrödinger–Poisson analysis suggested lowering of the effective barrier height by decreasing cap layer thickness is responsible for the Schottky degradation. When considering these experimental and theoretical findings, degradation mechanisms assuming diffusion of interfacial materials along dislocations are discussed. [ABSTRACT FROM AUTHOR]

The contact resistance of Mo-based ohmic contact was investigated for undoped GaN/AlGaN/GaN heterostructure field-effect transistors having different GaN cap layer thickness (tcap) and AlN mole fraction (xAl) values. Measured specific contact resistivity (\rhoc) exhibited a drastic increase by a factor of 10^3 by increasing tcap from 2 to 5 nm, and a minimum \rhoc value was 3.2\times 10^-7~\Omegacm^2 at T=300~K. We have developed a model of the ohmic contact assuming an n-type interfacial layer (donor density: Nd, thickness: td). Theoretical calculations suggested that the drastic increase of \rhoc by increasing tcap is due to td being between 2 and 5 nm. Also, the present model optimizing td and Nd values successfully explained measured trends of \rhoc with respect to tcap, xAl, and temperature. [ABSTRACT FROM AUTHOR]

This paper reports the theoretical and experimental study of the inverse piezoelectric effect in AlGaN/GaN heterostructure field-effect transistors (HFETs) with field plate (FP) electrodes. The theoretical analysis based on the 2-D Monte Carlo simulation predicted that introducing the FP structure drastically decreases the elastic energy due to the inverse piezoelectric effect. The extension of gate-connected or source-connected FP electrode and thinning a SiN film under FP were found effective to improve the critical voltage (Vcrit) for degradation under reverse bias stress. Also, calculated trends of Vcrit as a function of FP lengths and a SiN film thickness were qualitatively verified by step-stress measurements of field-plated HFETs fabricated on Si substrates. These results clearly indicate that the optimization of the FP structure minimizes degradation associated with the inverse piezoelectric effect in AlGaN/GaN HFETs. [ABSTRACT FROM AUTHOR]

In this letter, we have fabricated GaN hetero-structure field-effect transistors (HFETs) with submicrometer T-shaped gate on Si substrate to realize compact solid-state power amplifiers used in Ku-band and higher. An AlGaN buffer layer was incorporated under the GaN channel layer, which was expected to enhance the breakdown voltage without decreasing the gain. The fabricated GaN HFETs with a gate length (LG) of 0.16 \mum showed a three-terminal breakdown voltage (BV3) of 98 V and a peak maximum oscillation frequency (fMAX) of 226 GHz, with a simultaneous current gain cutoff frequency (fT) of 63 GHz at VDS=15~\rm V . In addition, a minimum noise figure (NF\min) of 1.01 dB with an associated gain of 16 dB at 14 GHz was obtained at VDS=5~\rm V . A 0.1-mm-wide GaN HFETs exhibited a saturated power density of 3.82 W/mm at VDS=30~\rm V , indicating the successful reduction of current collapse. To the best of our knowledge, this is the first demonstration of a GaN HFETs on Si, which combines high BV3 , high fMAX , high power density, and low NF\min at the Ku-band. [ABSTRACT FROM AUTHOR]