Improving the Performance of GaN Power Devices for High Breakdown Voltage and High Temperature Operation

tion as an alternative to Si as a semiconductor material for ultra-low-loss power devices. Early development of GaN was carried out in the area of light-emitting devices—green LEDs, lasers, etc.—but its superior performance as noted above and the needs of society led to R&D work for electronic devices being conducted world-wide. Specifically, the AlGaN/GaN HFET structure permits the formation of a high-density electron layer known as a two-dimensional electron layer on an AlGaN/GaN hetero interface by adding impurities to the carrier supply layer of AlGaN. Thus this AlGaN/GaN HFET structure holds out the possibility of achieving a high-frequency output device surpassing the characteristics of existing devices. Furukawa Electric has been involved in this development from the earliest stages, and has reported the world's first prototype inverter circuit using an AlGaN/GaN HFET. This inverter is made up of a DC converter using an AlGaN/GaN HFET and an AC inverter. Its operating output power was 50 W and maximum output power was 200 W 7). More recently a device with an output power in excess of 200 W has been reported 8), and its application as a high-output power device is anticipated. In this paper we describe the results of investigations in an AlGaN/GaN HFET, of, first of all, a Ti/AlSi/Mo structure for a unique ohmic electrode having reduced on-state resistance. We also describe how this ohmic electrode evolved into a larger device (gate width: 200 mm) and mounted in a package designed for operation in a hightemperature environment, and its characteristics at 500 K