We have epitaxially grown Si/ ␤-FeSi 2 /Si ͑SFS͒ structures with ␤-FeSi 2 particles on Si͑001͒, and SFS structures with ␤-FeSi 2 continuous films on both Si͑001͒ and Si͑111͒ substrates by molecular-beam epitaxy. All the samples exhibited the same photoluminescence ͑PL͒ peak wavelength of approximately 1.54 m at low temperatures. However, the PL decay times for the 1.54 m emission were different, showing that the luminescence originated from different sources. The decay curves of the SFS structures with ␤-FeSi 2 continuous films were fitted assuming a two-component model, with a short decay time ͑ ϳ 10 ns͒ and a long decay time ͑ ϳ 100 ns͒, regardless of substrate surface orientation. The short decay time was comparable to that obtained in the SFS structure with ␤-FeSi 2 particles. The short decay time was due to carrier recombination in ␤-FeSi 2 , whereas the long decay time was probably due to a defect-related D1 line in Si. We obtained 1.6 m electroluminescence ͑EL͒ at a low current density of 2 A / cm 2 up to around room temperature. The temperature dependence of the EL peak energy of the SFS diodes with ␤-FeSi 2 particles can be fitted well by the semiempirical Varshni's law. However, EL peak positions of the SFS diodes with the ␤-FeSi 2 films showed anomalous temperature dependence; they shifted to a higher energy with increasing temperature, and then decreased. These results indicate that the EL emission originated from several transitions.

Intentionally undoped p-type β-FeSi2 thin films were grown on Si(111) substrates by molecular-beam epitaxy using low-purity (4N) and high-purity (5N) Fe sources to investigate the effect of using a high-purity Fe source on the electrical properties of β-FeSi2. The hole mobility increased and the hole density decreased greatly as the annealing temperature and time were increased, particularly for the β-FeSi2 films produced using 5N-Fe. The observed temperature dependence of the hole mobility was reproduced well by considering various carrier scattering mechanisms due to acoustic-phonon, polar-optical phonon, nonpolar-optical phonon, and ionized impurities.

Plasmas with high ion-temperature of several keV and strong temperature anisotropy of more than 10 have been produced by using ion-cyclotron range of frequency (ICRF) heating in the GAMMA 10 tandem mirror. In such high performance plasmas with strong anisotropy, high-frequency fluctuations, so-called Alfvén-Ion-Cyclotron (AIC) waves, are spontaneously excited. The AIC waves have several discrete peaks in the frequency spectrum. Couplings between ICRF waves for heating and excited AIC waves are clearly observed in the central cell of GAMMA 10. Low frequency waves which have differential frequencies between discrete peaks of the AIC waves are also observed. Parametric decay of ICRF waves are discussed and pitch angle scattering of high-energy ions owing to those low-frequency waves are clearly detected. Energy transport along the magnetic field line is one of the important subjects when the ICRF power is injected in the perpendicular direction to magnetic field line.

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Spatiotemporal behavior of Alfvén-ion-cyclotron (AIC) waves excited in GAMMA10 is investigated using a microwave reflectometer and magnetic probes located at the edge. The frequency spectrum of the AIC waves has several discrete peaks. Simultaneous measurement of the internal density fluctuation and edge magnetic fluctuation of AIC waves shows that AIC waves have different radial structures in the initial excitation phase, but in the later steady state, each of them has the same structure in the radial direction. The results indicate that several AIC waves are excited as the same eigenmode in the radial direction.