Low on-resistance and high-breakdown-voltage AlGaN/GaN heterostructure field-effect transistors (HFETs) on Si substrate were fabricated. To improve the breakdown voltage of HFET, the total thickness of epitaxial layers was increased and the gate-to-drain spacing was expanded. As a result, the fabricated AlGaN/GaN HFETs with a gate width of 516 mm exhibited a breakdown voltage of 750 V, an on-resistance of 20 m, and a maximum drain current of more than 170 A. The on-resistancearea product (R on  A) was 0.26 Ámm 2 . This value was approximately 1/30 compared with that of conventional Si metaloxide-semiconductor field-effect transistors (MOSFETs).
The normally-off AlGaN/GaN HFETs on Si substrate were fabricated. To realize normally-off characteristic, recess was formed under the gate electrode and NiOx was formed as a gate electrode. As a result, the fabricated AlGaN/GaN HFET with a gate width of 157 mm exhibited a threshold voltage of +0.8 V, a breakdown voltage of more than 800 V, an onresistance of 72 mΩ, and a maximum drain current of more than 20 A. The on-resistance-area product (Ron×A) was 0.28 Ω・ mm 2 . This value is approximately 1/28 compared with that of conventional Si MOSFETs. The gate leakage current was decreased about four orders of magnitude smaller than the conventional normally-on HFETs. The NiOx gate electrode operates as a p-type material.
We demonstrated AlGaN/GaN heterostructure field-effect transistors (HFETs) grown on 2 inch Si (111) substrates by metalorganic chemical vapor phase epitaxy (MOVPE). Using GaN/AlN multilayers, we successfully fabricated nonpitted and crack-free GaN films thicker than 1 µm on Si substrates. An electron mobility of 1200 cm2/V·s, a sheet carrier density of 4.5 ×1012 /cm2, and a sheet resistance of 1100 Ω/sq were obtained. Fabricated 60-mm-gate-width HFETs exhibited a maximum drain current of more than 10 A, an on-state resistance of 0.5 Ω, and a breakdown voltage of more than 350 V.
A new device of high-power AlGaN/GaN heterostructure field-effect transistors (HFETs) fabricated on a Si substrate is proposed. Its application of the power factor correction (PFC) circuit is presented for the first time. The AlGaN/GaN HFETs fabricated on the Si substrate with a gate width of 152 mm exhibited a breakdown voltage of more than 800 V, an onresistance of 65 m, and a maximum drain current of more than 50 A. As for the results of the experiment on the PFC at 200 W and f ¼ 109 kHz, a power conversion efficiency of 95.2% was obtained. This value was about 1% higher than that of the PFC-circuit-using Si devices.
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