"Insulated gate structures on GaN and their interface properties"

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For the application to high-power/high-frequency electronic devices, we have investigated the formation processes of insulated structures on GaN and their interface properties. The main results obtained are listed below :(1) Chemistry and electronic properties of GaN surfaces after various kinds of surface treatments were characterized by x-ray photoelectron spectroscopy (XPS). Strong upward band bending of 1.4 eV was found at the air-exposed GaN surface. This is due to the high density of surface states. The surface treatment in the NH_40H solution and the ECR-excited N_2 plasma significantly decreased the surface band bending to 0.5 eV, indicating the reduction of the Fermi level pinning.(2) We have successfully fabricated the SiN_χ gate structure on the treated n-GaN surface by the ECR-CVD process. The SiN_χ/n-GaN structure showed the type-I band lineup and a low interface state density distribution in the range of 10^<11> cm^<-2> eV^<-1>. The surface passivation utilizing the ECR-C … More VD SiNx film enhanced the drain saturation current and improved the stability in the GaN/AlGaN heterostructure field effect transistors.(3) Electrical characterization of AlN/GaN interfaces was carried out by the C-V technique in samples grown by metal organic chemical vapor deposition. A low value of interface state density D_<it> of < 1x 10^<11> cm^<-2> eV^<-1> was achieved around the energy position of Ec-0.8eV. This indicates that the AlN/GaN structures have good interface properties with low interface state density, and are very promising for advanced MIS devices.(3) A novel surface passivation process for AIGaN/GaN heterostructures utilizing an ultrathin Al_20_3 layer (〜1 nm) was proposed. The reverse leakage current for the Schottky gate contact on the Al_20_3-passivated heterostructure surface was reduced by three orders of magnitude than that for the conventional Schottky gate structure. C-V results showed good gate controllability of two-dimensional electron gas (2DEG) by the novel gate structure. Less