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We report AlGaN-GaN high electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on SiC substrates with excellent microwave power and efficiency performance. The GaN buffers in these samples were doped with carbon to make them insulating. To reduce gate leakage, a thin silicon nitride film was deposited on the AlGaN surface by chemical vapor deposition. At 4 GHz, an output power density of 6.6 W/mm was obtained with 57% power-added efficiency (PAE) and a gain of 10, dB at a drain bias of 35 V. This is the highest PAE reported until now at 4 GHz in AlGaN-GaN HEMTs grown by MBE. At 10 GHz, we measured an output power density of 7.3 W/mm with a PAE of 36% and gain of 7.6 dB at 40-V drain bias.

A high-performance N-face GaN metal-insulator-semiconductor high-electron-mobility transistor was fabricated. A dual-AIN back-barrier scheme was developed using polarization engineering to provide a large total dipole moment, which allowed enhanced modulation doping for a higher 2-D electron gas density without parallel conduction. Devices with 0.6-μm gate length showed an fτ and fmax of 17 and 58 GHz, respectively. A highest power-added efficiency (PAE) of 71% at 4 GHz was measured in these devices with 20-V drain bias. At 28 V, an output power density of 6.4 W/mm with 67% PAE was achieved. [ABSTRACT FROM AUTHOR]

The performance of AIGaN/GaN high-electron-mobility transistors (HEMTs) on diamond and SiC substrates is examined. We demonstrate GaN-on-diamond transistors with periphery WG = 250 μm, 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. [ABSTRACT FROM AUTHOR]

High power-added efficiency (PAE) (≈74%) and r f-power (20 W/mm) operation of Schottky and insulated-gate AIGaN/GaN heterostructure field-effect transistors (HFETs) is reported at 2 GHz. In the pinched-off mode of operation, the PAE increases from a value of 55% to 74% when the drain bias is changed from 35 to 60 V. While both the Schottky and the insulated HFETs show high powers and PAE values, only the insulated-gate devices are stable at 20-W/mm output powers during a 60-h continuous wave r f-stress test. Their power drop of less than 0.1 dB is much smaller than the 0.8-dB drop for identical geometry Schottky-gate HFETs. The superior stability of the insulated-gate HFETs is attributed to the low forward gate currents. [ABSTRACT FROM AUTHOR]

Silicon carbide (SIC) MESFETs were fabricated using a standard SiC MESFET structure with the application of the ‘buried-channel’ and field-plate (FP) techniques in the process. FPs combined with a buried-gate are shown to be favorable concerning output power density and power-added efficiency (PAE), due to higher breakdown voltage and decreased output conductance. A very high power density of 7.8 W/mm was measured on-wafer at 3 GHz for a two-finger 400-μm gate periphery SiC MESFET. The PAE for this device was 70% at class AB bias. Two-tone measurements at 3 GHz ± 100 kHz indicate an optimum FP length for high linearity operation. [ABSTRACT FROM AUTHOR]

An experimental study of the mechanism of RF current collapse removal in high-power nitride-based HFETs is presented. The results show that the conductivity of the dielectric material under the field plate plays a crucial role in the current collapse removal. Identical geometry field plated HFETs differing only in the FP dielectric conductivity show varying degree of current collapse removal. Devices with semiconducting dielectric layers exhibit perfectly linear RF power - drain bias dependence with the output powers of 20 W/mm at 55 V drain bias with essentially no current collapse. A trapped charge discharging model is presented to explain the removal of current collapse in FPd devices. [ABSTRACT FROM AUTHOR]

We report for the first time the dc and radio frequency (RF) operation of a field-plated GaN-AlGaN metal-oxide-semiconductor heterostructure field effect transistor (MOSHFET). At 2 GHz and an RF output power level of 19 W/mm (drain bias 55 V), the device exhibited a remarkably stable operation for times in excess of 100 h. In contrast, a similar geometry HFET from the same wafer continuously degraded from 17 W/mm down to 14 W/mm within the first 20 h. We attribute the stable performance of the MOSHFET at high microwave powers to the extremely low gate-leakage currents and the current collapse-free operation resulting from the field-plated design. [ABSTRACT FROM AUTHOR]

High power microwave AlGaN-GaN high electron-mobility transistors (HEMTs) on free-standing GaN substrates are demonstrated for the first time. Measured gate leakage was -2.2 µA/mm at -20 V and -10 µA/mm at -45 V gate bias. When operated at a drain bias of 50 V, devices showed a record continuons-wave output power density of 9.4 W/mm at 10 GHz with an associated power-added efficiency of 40%. Long-term stability of device RF operation was also examined. Under room conditions, devices driven at 25 V and 3-dB gain compression remained stable in 200 h, degrading only by 0.18 dB in output power. Such results illustrate the potential of GaN substrate technology in supporting reliable, high performance AlGaN-GaN HEMTs for microwave power applications. [ABSTRACT FROM AUTHOR]

We report AlGaN-GaN high electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on SiC substrates with excellent microwave power and efficiency performance. The GaN buffers in these samples were doped with carbon to make them insulating. To reduce gate leakage, a thin silicon nitride film was deposited on the AlGaN surface by chemical vapor deposition. At 4 GHz, an output power density of 6.6 W/mm was obtained with 57% power-added efficiency (PAE) and a gain of 10 dB at a drain bias of 35 V. This is the highest PAE reported until now at 4 GHz in AlGaN-GaN HEMTs grown by MBE. At 10 GHz, we measured an output power density of 7.3 W/mm with a PAE of 36 % and gain of 7.6 dB at 40-V drain bias. [ABSTRACT FROM AUTHOR]