Study on GaN-based normally-off device on Si substrate using selective area growth

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GaN-based HEMTs have attractive for high power switching applications. Normally-off operation was one of major requirements for AlGaN/GaN HEMTs. However, realization of normally-off operation with high drain cuurent is difficult due to the existence of two-dimensional electron gas in heterointerface induced piezo and spontaneous polarization charges. Selective area growth (SAG) technique is one of solutions for normally-off operation.In this study, I report normally-off AlGaN/GaN HEMTs with SAG of an AlGaN layer and deposition of an Al2O3 film on an AlGaN/GaN heterostructure designed to be completely depleted. Adopting AlGaN regrowth in a selective area and Al2O3 film deposition for the access region of the HEMT, the normall-off operation of AlGaN/GaN HEMT was demonstrated. The device showed the drain current density of 160 mA/mm and the threshold voltgae of 0.4 V.