Development of ‡V-Nitride Based Electron Devices
Katsunori NISHII, Yoshito IKEDA, Hiroyuki MASATO, Toshinobu MATSUNO and Kaoru INOUE
Abstract: Wide band gap semiconductors such as III-V nitride materials and SiC have higher breakdown fields, higher electron saturation velocities and higher thermal conductivity than those of Si and GaAs. These attractive material properties are suitable for high power devices operating at high supply voltages. GaN-based electron devices are especially promising for high frequency operation because modulation-doped AlGaN/GaN heterostructure with high electron mobility is available. Besides, the density of the two dimensional electron gases at the heterointerface is very high owing to the piezoelectric and spontaneous polarization effects. These heterostructures are grown on either sapphire or SiC substrates since no bulk GaN substrate is commercially available widely. For sapphire substrates, the thermal conductivity is relative low, which leads to the reduction of drain currents in the regions of high drain current and high drain voltages due to the self-heating effects. Thus the AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) grown on SiC substrates with high thermal conductivity are more suitable for high power device applications. This paper describes the improvements of process technologies and fabrication of the devices. The fabricated 0.3ƒÊm gate HFETs showed a maximum drain current of 740mA/mm, a peak transconductance of 150mS/mm and a breakdown voltage higher than 50V. The cut-off frequency fT and maximum oscillation frequency fMAX were 22GHz and 85GHz, respectively. The fT and fMAX were almost constant with the increase of drain voltage up to 30V. The output power of 1W/mm at 1.9GHz was obtained. And then frequency dispersion was not observed with the high voltage operation. These results indicate that AlGaN/GaN HFETs grown on SiC substrates are quite suitable for high frequency microwave and millimeter-wave devices. Key Words:Wide band gap, AlGaN/GaN heterostructure, Heterostructure field effect transistor, Power device, Breakdown voltage, Frequency dispersion