The surrounding-field effect in a multi-mesa-channel (MMC) with an AlGaN/GaN structure, in which a periodic trench structure is fabricated directly under a gate electrode, was successfully observed. This effect resulted in a shallower threshold voltage, a smaller subthreshold slope, and a higher current drivability of a high electron mobility transistor (HEMT) than those of a standard planar-type HEMT. In addition, the MMC HEMT showed a low knee voltage, even with a wide spacing between the gate and drain electrodes. Excellent current stability in the saturation region of the MMC HEMT, probably due to the effective radiation of heat from both mesa sides of the channel, was also observed. Both planar and MMC HEMTs showed similar breakdown voltages under off-state operation, indicating no significant degradation in the breakdown characteristics of AlGaN/GaN HEMTs with a periodic trench structure in the gate region.

University. His research interests included surface passivation and device processing technologies for III-V compound semiconductors. Currently, his major activity expanded into characterization and control of surfaces and interfaces of GaN and related materials and their application to GaN-based electron devices. He has authored or co-authored over 160 papers in scientific and technical journals.

No abstract

No abstract

A selective electrochemical oxidation has been applied to the AlGaN surface to fabricate a recessed-oxide-gate structure for normally-off AlGaN/GaN high-electron-mobility transistors (HEMTs). We observed bias-dependent oxidation current characteristics peculiar to the AlGaN/GaN heterostructure. A flat interface between the oxide and AlGaN was confirmed by cross-sectional transmission electron microscopy. The selective formation of the recessed oxide allowed the local depletion of two-dimensional electron gas at the AlGaN/GaN interface and thus the achievement of normally-off operation. The recessed-oxide-gate HEMT with the oxide thickness of 20 nm showed good gate control of drain current with the threshold voltage of +1.2 V.