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A hybrid Schottky–ohmic drain technology for millimeter-wave (mmW) AlGaN/GaN high-electron-mobility transistors (HEMTs) is proposed. The Schottky metal extension in the ohmic region of drain reduces the actual source–drain spacing, resulting in a smaller ON-resistance and a higher maximum current. Extended Schottky metal in the drain region modulates the electric-field distribution, thereby leading to an improved breakdown voltage, suppressed current collapse, and high reliability. Compared with the ohmic drain, the current gain cutoff frequency (${f}_{T}$) was improved from 64 to 76 GHz, and the maximum oscillation frequency (${f}_{\text {max}}$) was improved from 125 to 157 GHz, resulting from the decreased parasitic drain resistance (${R}_{d}$). Moreover, large-signal measurements in continuous wave (CW) at 30 GHz demonstrated a peak power-added efficiency (PAE) of 45.5% and a saturated output power density (${P}_{\text {sat}}$) of 8.5 W/mm at ${V}_{\text {ds}}= {30}$ V. In addition, the direct current (DC) and radio frequency (RF) characteristics showed a negligible degradation after large-signal measurements at 30 GHz. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Si-rich SiN/Si3N4 bilayer passivation were studied in this article. The use of a Si-rich SiN interlayer leads to improved channel transport property, current collapse, power performance, and temperature-dependent stability. Devices without Si-rich SiN interlayer passivation exhibit an increase in the gate leakage current by over three orders of magnitudes with temperature increasing from 300 to 420 K, leading to an increase in a current collapse from 9.7% to 24.7%, while the devices with Si-rich SiN passivation exhibit a weak temperature dependence of leakage current and a constant current collapse about 5%. Small signal characterization shows that Si-rich SiN passivation results in a remarkable decrease in the effective gate length by ~15% with temperature up to 420 K. At 17 GHz, devices with Si-rich SiN interlayer passivation exhibit an output power density of 7 W/mm and a peak power-added efficiency (PAE) of 56%. The improved power performance of devices using Si-rich SiN interlayer passivation is attributed to the suppressed current collapse and superior device stability under high channel temperature. [ABSTRACT FROM AUTHOR]

In this work, the performance of AlGaN/ gallium nitride (GaN) high-electron mobility transistors (HEMTs) with different Fe doping tails was systematically investigated and compared. It is illustrated that the combination of the unintentionally doped (UID) GaN layer and a thinner Fe doping buffer layer would result in a faster slope rate of Fe concentration in the UID GaN layer. The devices with the fastest slope rate of Fe concentration in the UID GaN layer exhibited excellent large signal performance, including the saturated power density (${P}_{sat}$) of 9 W/mm and the power-added efficiency (PAE) of 65.6%. In addition, the ${P}_{sat}$ and the PAE of the device with the fastest slope rate of Fe concentration in UID GaN layer are 27.7% and 14.7%, which are higher than that of the device with the slowest slope rate of Fe concentration under the class AB operation conditions. Pulse ${I}$ ,– ${V}$ measurement results demonstrated that the buffer-related current collapse was more effectively suppressed in the 0.5- $\mu \text{m}$ Fe doping buffer layer because of faster slope rate of Fe concentration in UID GaN layer. Moreover, the frequency-dependent capacitance and conductance measurement results indicated that the current collapse was relevant to deep traps in the UID GaN layer introduced by Fe doping. By reducing the concentration of the deep traps caused by Fe doping, the device showed excellent characteristics of dc and RF. Furthermore, controlling the Fe doping tail was important for designing the GaN-based power amplifier with high ${P}_{sat}$ and PAE. [ABSTRACT FROM AUTHOR]