2 . Fabrication of Mesfet for High - Current Operation

In the 21st century, environmental measures such as reducing CO2 emissions have been demanded in energy development. Si switching devices are generally used as electric power converting devices. To reduce power loss, the density of Si device integration has become satisfactorily high. As a result, the on-state resistance of a Si metal oxide semiconductor field effect transistor (MOSFET) reached the theoretical limit of Si. On the other hand, wide bandgap semiconductors such as SiC, GaN, and diamond also have a wide bandgap, small atomic binding distance, large binding energy (strong for radiation damage), and thermal stability. They therefore have great potential as hard electronic materials which exceed Si . Suitable material properties for a hard electronic material include breakdown electric field, saturation velocity, thermal conductivity, mobility, and dielectric constant. Figures of merit 2~6) combined with these material properties for high power, high speed, high frequency, and low loss have already been reported. GaN also has excellent figures of merit compared with those of Si and GaAs . In particular, it should be noted that the on-state resistance of GaN FET can be remarkably reduced to less than that of Si MOSFET by a two or three order of magnitude, and GaN FET has potential for low-loss and cooling free power switching devices and inverters, which are difficult to realize using Si devices. The uses of high-temperature devices are high-temperature sensor, aircraft, space rocket engine controller, atomic energy equipment, and measuring instruments for underground exploration. The good features of high-temperature operation devices are that they do not require a large cooling system to suppress heat (or the cooling system is very small). Recently, GaN electronic devices have been actively developed in the U.S.A. Also in the U.S.A., several venture companies selling and manufacturing GaN electronic devices have recently been established. Furthermore, Air Force and Naval Research have also been actively researching military applications. Other uses of GaN electronic devices are electric power switching devices such as inverters, converters, relay switching devices, and high-frequency devices. Among high-temperature operation devices, metal semiconductor field effect transistors (MESFET) , hetero field effect transistors (HFET) , and modulation doped field effect transistors (MODFET) 12) have already been reported. Not only in the U.S.A. but also in Japan, highfrequency devices such as high electron mobility transistors (HEMT) and HFET using an AlGaN/GaN heterostructure and two-dimensional electron gas (2DEG) have been developed, and the maximum frequency for operation is over 130 GHz. This report describes the fabrication of AlGaN/GaN power HFET and how we obtained a very low on-state resistance (2 mΩcm2) with a value that corresponds to one-quarter of that of Si MOSFET. Furthermore, it is reported that AlGaN/GaN HFET was operated under conditions of 20 A, and the maximum Schottky breakdown voltage of gate and source was 600 V. AlGaN/GaN Power FET