It is found that dislocation-free silicon crystal growth is possible without a thin neck proposed by Dash at 40 years ago and established as the critical step to obtain dislocation-free silicon crystal. Three kind of dislocations which are formed due to thermal shock, lattice misfit and incomplete seeding must be suppressed to grow dislocation-free crystals without the thin neck. It is shown that seed crystals heavily doped with B, Ge or In are useful to suppress dislocation generation due to thermal shock and seed crystals codoped with B and Ge are useful to suppress dislocation generation due to lattice misfit. The seeding conditions such as temperature and pulling rate which result in a shape of crystal grown are discussed to avoid dis-location formation due to incomplete seeding. Finally, industrial scale silicon crystals with 8 inches in diameter are successfully grown without the thin neck.
Propagation behavior of dislocations and surface morphological evolution are crucial factors to determine the quality of heteroepitaxial films on substrates. We report here a novel method applicable to form high-quality strainrelaxed Si_<1-x>Ge_x. buffer layers on Si(001) substrates. In this method, strain relaxation of the Si_<1-x>Ge_x layer is performed with two-step procedures consisting of high temperature annealing of the first pseudomorphic Si_<1-x>Ge_x layer and epitaxial growth of the second Si_<1-x>Ge_x layer on the partially relaxed first layer. The formation of a thin cap-layer before the annealing is effective in suppressing surface roughening during the annealing. In this case, penodic undulation formed on the second layer surface the key to enhancing the glide of threading terms of misfit dislocations, which results in a drastic reduction in the threading dislocation density.
Silicon carbide (SiC) is the most promising material for high power, high frequency and low loss device applications. In order to realize SiC devices, it is necessary to improve the grown crystal quality. SiC bulk single crystal is grown by sublimation method, inside a closed carbon crucible. Because of the black box process, the optimization of sublimation process is difficult. From this point view the in situ X ray topography system was developed to observe the phenomena inside a crucible during the growth. The numerical simulation was also applied. From these observations, the heat and mass transfer in a crucible was discussed involving in the macroscopic crystal quality, such as crystal diameter, growing surface shape, and also in the microscopic crystal quality such as defect generations.
The growth of bulk GaN single crystals by the high-pressure solution growth method under "the Light for the 21st Century" Japanese national project has been carried out using a high-pressure furnace. It was found that the rate of increase of N_2 pressure affected the size of a GaN single crystal. GaN single crystals with an area of about 120 mm^2 were obtained at a rate less than 49 MPa/h. The maximum size of single crystals grown at 1475℃ under a N_2 pressure of 1000 MPa was over 20 mm in diameter. The FWHM of rocking curve measured for (0002) X-ray diffraction peak was 60-120 arcsec and (101^^-1) X-ray diffraction peak was 30-60 arcsec. The dislocation density less than 10^5 cm^<-2> was obtained by TEM image and CL image observations.
We investigated an effect of intense short pulse laser irradiation on organic and protein crystallization in supersaturated solution. Crystallization of an organic molecule, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) , was observed when an intense YAG laser was irradiated to its supersaturated solution. An effective crystallization of a protein, lysozyme, was confirmed by applying an intense femtosecond laser, although the crystal was not observed with the intense YAG laser irradiation. These results indicate that the nucleation strongly depends on the laser conditions. The crystallization will be promoted by nonlinear phenomena of the femtosecond laser whose peak intensity is over GW.