Nariaki Ikeda, Jiang Li, Sadahiro Kato, Mitsuru Masuda and Seikoh Yoshida
GaN electron devices are expected to contribute significantly toward efficiency improvement and downsizing of power supplies since the devices have the potential of realizing higher breakdown voltages and lower on-state resistances in comparison to Si electron devices conventionally used. The authors have investigated, by thinning the AlGaN layer and simultaneously inserting an AlN layer, GaN/AlGaN heterojunction Field Effect Transistor (HFET) structures aimed at realization of normally-off type devices that are high in breakdown voltage yet comparatively low in on-state resistance characteristics. And, using AlGaN/GaN heterostructure epitaxial layers on a Si substrate-- one of the prerequisites for cost reduction, normally-off operation with a threshold voltage of 0 V has been achieved. A proprietary diode structure has also been proposed to enable loss reduction, and operation with a low on-state voltage has been confirmed where a current begins to flow at approximately 0 V. Moreover, an epitaxial AlGaN structure with a reduced thickness has been applied to this structure, and a diode featuring low leakage current as well as low on-state voltage operation has been obtained.