225nm UV light emitting BN at the room temperature prepared by laser-plasma synergetic deposition

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(1)We have carried out the research on a new type of BN, namely, sp^3-bonded 5H-BN, which was originally found at the NIMS for the first time and reported in 1999. This BN is prepared in the forms of powder as well as films by synergetic deposition methods using plasma and laser. This BN shows a UV emission sharply at 225nm and broadly at 300nm. The former band is observed only in the powder samples most, probably due to the high crystallinity. On the other hand, film samples show only the 300 nm broad band. It is noteworthy that both bands are excited at room temperatures. To achieve the final goal of application of these samples to UV light emission devices, it is important to understand the growth mechanism and the relationship between the structural characteristics and the UV properties.(2)Since the structural properties originate from the growth dynamics, we invented a new in-situ observation method of the growth rates of films by utilizing photoluminescence (PL) from the samples … More excited by the processing excimer laser. We could find the transition of the growth mode from initial fibrous growth to the micro-cone formation at the mid stage by scanning electron microscopy and the corresponding change of the growth rate was clearly seen in the in-situ PL observation.(3)As for the growth of powder samples, we observed transmission electron microscopic (TEM) images corresponding to some different stages of the growth. Based on them, we concluded the existence of a precursor which is most likely in the supercritical fluid state of BN. We built a growth model using the mathematics of 2-dimensional nonlinear dynamical system, and by which we showed a synergetic effect of plasma and laser to induce the nonequilibrium phase formation of sp^3-bonded 5H-BN.(4)As for the film growth mechanism, based on experimental observations, we could demonstrate that it was a photochemically-activated growth where precursor radicals were supplied from a plasma. We build a model where forced-oscillatory photochemical reactions compete with surface diffusion of the precursor radicals. By the model, we could explain the temperature-dependent uniform-fractal transition of the micro-cone distribution observed on Si(100) substrates, and the origin of the observed fractal morphology.(5)The lifetime of the UV emission was short enough to indicate that this material is a direct-transition semiconductor and applicable to future solid state UV LED. Less