A High-Power AlGaN/GaN Hetero Field-Effect Transistor
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A High-Power AlGaN/GaN Hetero Field-Effect Transistor
Seikoh Yoshida and Hirotatsu Ishii Yokohama R&D Laboratories, The Furukawa Electric Co., Ltd 2-4-3, Okano, Nishi-ku, Yokohama, 220-0073 Japan
ABSTRACT
An AlGaN/GaN hetero field effect transistor (HFET) was operated at 20 A. Its on-state resistance was lower than that of a Si-based FET. GaN and related materials were grown by gas-source molecular beam epitaxy (GSMBE). Sapphire substrates were used for GaN growth. An undoped GaN/Al0.2Ga0.8N heterostructure was grown on the substrate. The sheet carrier density of two dimensional electron gas was 1x1013 cm2 and the mobility was 1200 cm2/Vs at room temperature. The breakdown field of undoped high resistive GaN layer was about 2.0 MV/cm. Al0.2Ga0.8N/GaN HFET for a large current operation was fabricated. The gate width was 20 cm and the gate length was 2000 nm. The electrode material of the source and the drain was Al/Ti/Au and the Schottky electrodes were Pt/Au. The distance between the source and the drain was 6000 nm. The maximum breakdown voltage of gate and source was 600 V. The on-state resistance of the HFET was about 2 mohm•cm2 at 100 V. The transconductance (gm) of this HFET was about 120 mS/mm. It was confirmed that the HFET with a gate width of 20 cm could be operated at the condition of a large current operation.
INTRODUCTION
Wide band gap semiconductors such as GaN are very attractive for electronic devices that can operate under high-temperature, high-power and high-frequency conditions [1]. That is, GaN and related materials have a large figure of merit for those purposes, since they have a wide band gap, a high breakdown electric field and a high saturation velocity. Especially, it is expected that the specific on-state resistance (Ron) of the field-effect transistor (FET) is lower than that of Si or GaAs. The AlGaN/GaN heterostructure is expected to have a high electron mobility and high carrier density of two dimensional electron due to a large piezo-electric field effect. The AlGaN/GaN hetero field effect transistor (HFET) can be expected to be operated at large currents. Recently, it has been actively reported that high-temperature, high-power and high-frequency devices using GaN and related materials have been operated [2-11]. However, there has not yet been experimentally reported concerning the on-state resistance of GaN devices. We have recently reported that the AlGaN/GaN HFET could be operated above 10 A [12]. In this paper, it is reported that the an AlGaN/GaN heterostructure was formed by gas source molecular beam epitaxy (GSMBE), and that the FET was operated at a current of over 20 A with an on-state resistance of a unit HFET for a large current operation was lower than that of conventional Si devices.
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EXPERIMENTAL An AlGaN/GaN heterostructure was grown using a GSMBE [7]. At first, a Ga-rich surface was formed on a sapphire substrate surface. A 50 nm-thick GaN buffer layer was next formed on a Ga-rich surface at 973 K. A thick film of GaN was grown using Ga and ammonia gas o
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