Halide vapor phase epitaxy (HVPE) is the most promising method for obtaining bulk GaN, and a 2 inch free standing wafer has been already obtained by growing on a sapphire substrate and separating by laser irradiation. It is, however, neither very easy nor very productive. Here we propose another more productive way of growing on GaAs substrate, though a free standing GaN is not yet perfectly obtained. It was found that hexagonal GaN with a smooth surface can be grown on GaAs (111) substrates at as high as 1000 by introducing GaN layer grown at an intermediate temperature such as 850. Surface of the GaN layer grown at 850 was rough but it became smooth surface when GaN was grown on it at 1000, though sometimes there were several hexagonal pits on the surface. The θ-2θ and ω X ray diffraction (XRD) of the grown layer showed only hexagonal GaN(0002).

The transistor action with negative differential resistance (NDR) of a nanometer-thick metal (CoSi2)/insulator (CaF2) resonant tunneling transistor is discussed for two transistor structures. These transistors are composed of metal-insulator (M-I) heterostructures with two metallic (CoSi2) quantum wells and three insulator (CaF2) barriers grown on an n-Si (lll) substrate. One of the two structures has the base terminal connected to one of the quantum wells next to the collector, and the other, to one next to the emitter. Although base resistance is high maybe due to the damage caused during the fabrication process, the two transistors show different characteristics, as expected theoretically. Transfer efficiency α (= IC/IE) close to unity was obtained at 77 K for electrons through the resonant levels in M-I heterostructures.