Fabrication of a High-Power GaN Metal Semiconductor Field-Effect Transistor
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FABRICATION OF A HIGH-POWER GaN METAL SEMICONDUCTOR 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
A high-power metal semiconductor field-effect transistor (MESFET) for operating at a very large-current using GaN is reported for the first time. GaN was grown by metalorganic chemical vapor deposition (MOCVD). Sapphire substrates were used for GaN growth. A GaN MESFET with a large size was fabricated. Multi-finger gates were used for large-current operation. The total gate width was 8 cm and the gate length was 2 µm. The electrode materials of the source and the drain were Al/Ti/Au and the schottky electrodes were Pt/Au. The gate, source, and drain were isolated using SiO2. An FET structure was fabricated using a dry-etching technique. Multi-electrode structures were also fabricated using SiO2 for isolating the source, drain, and gate electrodes, respectively. The FET was operated at a current of over 5 A. The breakdown voltage was over 500 V. The transconductance (gm) was about 12 mS/mm. The pinch-off voltage was about -8 V. We confirmed that this GaN MESFET can also be operated at a current of 10 A.
INTRODUCTION
GaN and related materials are very promising for electronic devices which can operate under high-power, high frequency, and high-temperature [1]. GaN and related materials have large figures of merits for these purposes compared with conventional Si or GaAs devices, since these materials have a wide band gap, a high breakdown electric field, and a high saturation velocity [1]. Those GaN electronic devices for high-temperature and highfrequency operation have recently been reported [2-8]. We have also demonstrated a GaN metal-semiconductor field-effect transistor (MESFET) and a bipolar junction transistor (BJT) which can be operated at 673 K and 573 K, respectively [9-11]. The high-temperature reliability of these GaN electronics was also confirmed. However, GaN devices for large-current operation have not been reported until now. In this paper, we report on the fabrication of a GaN MESFET with large-current operation.
EXPERIMENTAL PROCEDURE
In order to fabricate the GaN MESFET, GaN was grown on a sapphire substrate having a 2-inch diameter by metalorganic chemical vapor deposition (MOCVD). A 50 nm-thick GaN buffer layer was first formed on the substrate using ammonia (NH3) as a nitrogen source and trymethylgallium (TMG) at lower temperature, such as 873
G13.4.1
K. An undoped 2000 nm-thick GaN layer with a high resistivity was grown on a GaN buffer layer at 1323 K in order to obtain a high-quality GaN active layer with a thickness of 200 nm. The GaN active layer with a carrier concentration of 2.0x1017 cm-3 and a mobility of 300 cm2/Vsec at room temperature were used to fabricate the MESFET. A 100 nm thick Si-doped layer is the contact layer. The Si concentration of the contact layer is 2x1019 cm-3. The root-mean-square (rms) showing a surface roughness of GaN became small
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