Kazuki Mizushima

Short lifetime photoluminescence of amorphous-SiNx films

We observed photoluminescence (PL) of amorphous-SiNx films which showed a short radiative lifetime of about 1 ns. The spectrum form is Gaussian centered at around 2.2 eV. The samples were prepared by low-pressure chemical vapor deposition with SiH2Cl2 and NH3 gases. We propose an electron-phonon coupling model for the PL, assuming that the coupling phonon is Si–H or N–H vibrational mode and the bond length changes over 0.1 A at an excited state due to the strong interaction.

Molecular beam epitaxy of highly [100]-oriented β-FeSi2 films on lattice-matched strained-Si(001) surface using Si0.7Ge0.3 layers

We have grown highly [100]-oriented β-FeSi2 continuous films on lattice-matched Si(001) surfaces using Si0.7Ge0.3 layers by molecular beam epitaxy (MBE). The β-FeSi2 films grown on the lattice-matched Si(001) did not aggregate even when it was grown at temperatures above 600°C. The omega-scan full width at half maximum of the β-FeSi2(800) peak was smaller than that of the film grown on Si(001) over the entire growth temperature ranging from 500 to 720°C. X-ray diffraction pole figure measurements revealed that a [100]-oriented β-FeSi2 template layer is necessary to obtain [100]-oriented β-FeSi2 films by MBE even on the lattice-matched Si(001).

Toward multiscale modelling: the role of atomistic simulations in the analysis of Si and SiC under hydrostatic compression

The structural responses of silicon and silicon carbide under hydrostatic compression have been analyzed by using Tersoff interatomic potential function. We show the elastic stability criteria, based on the elastic stiffness coefficients gives consistent predictions of critical pressures at which the lattices become unstable with molecular dynamics simulations. However, the predicted values are considerably higher than that of another prediction based on the thermodynamic criteria. By calculating activation barriers for the homogeneous silicon phase transition from cubic diamond to β-Sn, we suggest that the elastic and thermodynamic criteria give upper and lower bounds respectively on the transition pressure. We also show that the effect of the atomic size disparity between Si and C atoms can be dominant in favoring amorphization over polymorphic transition in silicon carbide.

Relationship Between Graded Layer Structures and Defects in Silicon-Germanium Virtual Substrates

Silicon-germanium virtual substrates have been synthesized by low-pressure chemical vapor deposition. We obtained threading dislocation densities ranging from 10 5 to 10 6 cm −2 , surface roughness ranging from 1.5 to 4 nm, and also cross-hatch pattern densities, depending on the grading rate and top layer germanium composition. For the typical sample, which has a linear-graded structure with a grading rate of 20%/[µm, and germanium composition of 30 % at the top layer, we obtained dislocation densities of about 10 6 cm −2 and root mean squared surface roughness of about 3 nm. The obtained dislocation densities are equivalent with the virtual substrates synthesized by ultra-high vacuum system. On the other hand the surface roughness is superior to the typical reported values. In this study three kinds of structures, i.e. linear-graded, stepwise, and graded-step structures, were considered. We found the defects are effectively reduced by introduction of an optimum number of steps in the graded layer.