Record performance of high-power GaN/Al 0:14 -Ga 0:86 N high-electron mobility transistors (HEMT's) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12 2 125 m), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the 02 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-Nitride HEMT under RF drive.
Microstructure of α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AlN (or GaN) buffer layers has been studied by transmission electron microscopy. The defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3〈112̄0〉 type, lying along the [0001] growth direction. The main sources of threading dislocations are the low angle grain boundaries, formed during coalescence of islands at the initial stages of GaN growth. The grain sizes range from 50 to 500 nm, with in-plane misorientations of less than 3°. The nature of these threading dislocations suggests that the defect density would not likely decrease appreciably at increasing film thickness, and the suppression of these dislocations could be more difficult.
The effect of ion-implantation-induced damage on the resistivity of n-type GaN has been investigated. H, He, and N ions were studied. The resistivity as a function of temperature, implant concentration, and post-implant annealing temperature has been examined. Helium implantation produced material with an as-implanted resistivity of 1010 Ω-cm. He-implanted material remained highly resistive after an 800 °C furnace anneal. The damage associated with H implantation had a significant anneal stage at 250 °C and the details of the as-implanted resistivity were sample dependent. N implants had to be annealed at 400 °C to optimize the resulting resistivity but were then thermally stable to over 800 °C. The 300 °C resistivity of thermally stabilized He- and N- implanted layers was 104 Ω-cm, whereas for H-implanted layers the 300 °C resistivity was less than 10 Ω-cm.
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