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We have investigated the formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas at pressures of 2-10 Torr. Growing process of silicon nanoparticles was observed by measuring light emission resulting from decomposition of the nanoparticles by using a second pulsed-laser. It was directly observed that the nanoparticles are formed on the time scale of 1 ms, depending on the ambient gas pressure. This information is expected to be quite helpful for growth control and for chemical surface-modification by using pulsed-laser light or by exposure to a pulsed reactive-gas jet. The nanoparticles exhibit visible photoluminescence after deposition. Effect of chemical modification to photoluminescence have been investigated. Brighter luminescence have been observed from silicon nanocrystallites precipitated in SiO2 films during annealing of SiOx films deposited using a laser ablation technique.

We have studied dynamical mechanism of laser ablation using combined time- and spatially-resolved measurements of laser plasma soft x-ray absorption spectroscopy and visible light emission imaging/spectroscopy. The obtained results indicate that there are no significant formation of silicon clustres and no growth of silicon nanoclusters till 2.55 ms after laser ablation. We have fabricated nanocluster-based silicon films by laser ablation in ambient gases and investigated photoluminescence at room temperature from the films. It is found that the growth of silicon nanocluster-based films with visible light emission can be well controlled by means of novel laser ablation methods.

We have found recently that there are optimum values of laser irradiation time and spot size for laser Solid Phase Epitaxial (SPE) growth of GaAs. The amorphous GaAs layers with a thick-ness of 600 @/Ar35@/ used in the study were produced by P+ ion implantation. Both 1.7W Ar ion laser and 4W Kr ion laser irradiations were used. The optimum values for SPE of the time and spot diameter were 67ms and 1 μm for the Ar ion laser and 17ms and 10 μm for the Kr laser. The 1 μm spot diameter is the smallest ever reported. For the Kr ion laser irradiation under these conditions, the speed of the laser SPE growth was as high as 30 μm/sec and the tempera-ture was as low as 560°C. The quality of the laser SPE growth layers was evaluated by the peak heights of the LO phonon Raman lines.

In order to clarify an influence of initial spin density or optical absorption coefficienton the pulsed-laser annealing effect, we have performed systematically ion backscatteringand channeling (RBS) analysis and ESR measurement as a function of spindensities in ion-implanted Si samples. An effect of implanted ion species has also beeninvestigated. It was found that the initial spin density can yield a good criterion forpredicting the annealing effect below implanted doses of 1×1016 /cm2 because the spindensity is strongly correlated with the optical absorption coefficient. From spindensitymeasurement, the initial absorption coefficient of as-implanted Si layer was foundto be a very important factor which dominates the effect of laser annealing even if thereis a nonlinear absorption mechanism. As to impurity effect, it was also clarified thatlaser annealing effects are much different among ion species. This seems to be duemainly to the difference of segregation coefficient of impurity in Si.

We have investigated non-equilibrium Si with extremely high impurity concentration of Te and Zn fabricated by means of pulsed-laser annealing and ion implantation. It was found that there exists a significant difference of segregation and lattice between II (Zn)-and VI (Te)-colum atoms after laser annealing. It was possible to dope subsititutional Te impurity up to some 5×1020/cm3 and fabricate the non-equilibrium Si: Te system with n-type conduction.