Power Performance of AlGaN/GaN HEMTs Grown on SiC by Ammonia-MBE at 4 and 10 GHz

In this letter, we report on the microwave power and efficiency performance of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by ammonia molecular beam epitaxy (ammonia-MBE) on SiC substrates. At 4 GHz, an output power density of 11.1 W/mm with an associated power-added efficiency (PAE) of 63% was measured at V _ds = 48 V on passivated devices. At 10 GHz, an output power density of 11.2 W/mm with a PAE of 58% was achieved for V _ds = 48 V. These results are the highest reported power performance for AlGaN/GaN HEMTs grown by ammonia-MBE and the first reported for ammonia-MBE on SiC substrates.     

High-power AlGaN/GaN HEMTs for Ka-band applications

We report on the fabrication and high-frequency characterization of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at V/sub DS/=30 V. Under similar bias conditions, more than 8.6 W/mm, with 32% PAE, were obtained on the MBE-grown sample. The dependence of output power, gain, and PAE on gate and drain voltages, and frequency have also been analyzed.     

Power performance of AlGaN-GaN HEMTs grown on SiC by plasma-assisted MBE

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.     

Nonalloyed ohmic contacts in AlGaN/GaN HEMTs by ion implantation with reduced activation annealing temperature

This letter reports AlGaN/GaN high-electron mobility transistors with capless activation annealing of implanted Si for nonalloyed ohmic contacts. Source and drain areas were implanted with an Si dose of 1/spl times/10/sup 16/ cm/sup -2/ and were activated at /spl sim/1260/spl deg/C in a metal-organic chemical vapor deposition system in ammonia and nitrogen at atmospheric pressure. Nonalloyed ohmic contacts to ion-implanted devices showed a contact resistance of 0.96 /spl Omega//spl middot/mm to the channel. An output power density of 5 W/mm was measured at 4 GHz, with 58% power-added efficiency and a gain of 11.7 dB at a drain bias of 30 V.     

Analysis of Transistor Failure in a Nuclear Environment

This paper describes a method for predicting transistor reliability as a function of nuclear radiation exposure, through the use of the Weibull distribution. Graphical plots of seven different types of transistors show ac gain degradation as a function of integrated neutron exposure. The plots on Weibull graph paper are extended to include probability of failure to 0.1 and 0.01 percent. The graphs are interpreted and the plotting technique and assumptions for extrapolation of the Weibull distribution are discussed.     

Application of Silicon Damage to Neutron Exposure Measurement

A technique is described for using the damage in silicon to measure neutron exposure in Radiation Damage Units (RDUs) with transistors called Radiation Damage Monitors (RDMs). The technique is useful in measuring the damage gradients across experiments and in determining the relative damage effect of a neutron environment. Two calibration procedures are described, as are the operating characteristics and use procedures for five transistor RDMs to cover the exposure range from 1011 to 1015 n/cm2.     

Unpassivated high power deeply recessed GaN HEMTs with fluorine-plasma surface treatment

In this letter, unpassivated high power deeply recessed GaN-based high electron mobility transistors (HEMTs) are reported. The introduction of a thick graded AlGaN cap layer and a novel fluorine-plasma surface treatment reduced the gate-leakage current and increased breakdown voltage significantly, enabling the application of much higher drain biases. Due to excellent dispersion suppression achieved at an epitaxial level, an output power density of more than 17 W/mm with an associated power added efficiency (PAE) of 50% was measured at 4 GHz and V/sub DS/=80 V without SiN/sub x/ passivation. These results demonstrate the great potential of this novel epitaxial approach for passivation-free GaN-based HEMTs for high-power applications.     

X- and Ka-band power performance of AlGaN/GaN HEMTs grown by ammonia-MBE

A report is presented on the power performance of deep submicron AIGaN/GaN high electron mobility transistors grown by ammonia molecular beam epitaxy. At 10 GHz, 70% power-added-efficiency (PAE) and 3 W/mm power density were demonstrated at a drain bias of 20 V. At 30 GHz, 31% PAE and 6.5 W/mm power density were achieved at a drain bias of 40 V.     

Radiation Tolerant Magnetic Amplifier

Several operational magnetic amplifier stages of low and medium power levels were designed and tested in a nuclear radiation environment to levels of 1 x 1016 neutrons/cm2 (E > 0.1 Mev) and were found to exhibit acceptable performance. Various diode characteristics were obtained under radiation to correlate behavior with amplifier designs. Diode test results are presented for irradiations at three different reactor facilities.