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A normally-off AlGaN/GaN MOS heterojunction field-effect transistor (MOS-HFET) with a recessed gate structure formed by selective area regrowth is demonstrated. The fabricated MOS-HFET exhibits a threshold voltage of 1.7 V with an improved hysteresis of 0.5 V as compared with a device fabricated by a conventional dry etching process. An analysis of capacitance–voltage (C–V) characteristics reveals that the dry etching process increases interface state density and introduces an additional discrete trap. The use of the selective area regrowth technique effectively suppresses such degradation, avoiding the MOS interface from being exposed to dry etching. The results presented in this paper indicate that the selective area regrowth technique is promising for the fabrication of normally-off AlGaN/GaN MOS-HFETs.

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In order to understand and to further optimize the silicon interface control layer (Si ICL)-based passivation process for GaAs, the effects of the initial surface reconstruction of GaAs on the microscopic surface structures of the Si ICL and on the macroscopic electronic properties are studied in situ, using an ultrahigh-vacuum (UHV) multi-chamber system. (2×4) and c(4×4) GaAs surfaces were prepared by molecular beam epitaxy (MBE). Surface structures and compositions were studied by UHV scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Macroscopic electronic properties of the passivated surfaces were investigated by XPS band bending measurements, UHV contactless capacitance-voltage (C-V) measurements and UHV photoluminescence (PL) methods. The Si layer grown on the initially reconstructed c(4×4) surface was found to be more ordered and flatter than that grown on the initially reconstructed (2×4) surface. This difference showed a strong correlation with the macroscopic electronic properties after the Si ICL-based passivation process measured by XPS, UHV contactless C-V and PL techniques. The results indicate the importance of the two-dimensional order on the Si-deposited surfaces for successful passivation.