Transient nucleation following pulsed-laser melting of thin silicon films

Influence of pulse duration on the amorphization of GeSb thin films under ultrashort laser pulses

“…24,25 The primary effect of reducing the pulse duration below 2 ps is to produce a strong increase in both the initial thermal gradient across the melt volume ͑the film is again completely melted͒ and the initial supercooling that leads to a sharp increase in the nucleation rate of the solid phase. The subsequent release of an enhanced amount of solidification heat increases the temperature of the surrounding liquid and slows down the bulk solidification process 17,18 in a similar manner to what happens when the film thickness is increased as reported earlier. 16 In conclusion, a minimum amorphization time close to 400 ps is achieved when irradiating c-GeSb films with pulse durations in the range 5-20 ps.…”

“…From these results, the authors concluded that bulk solidification was the dominant mechanism in these films under ps laser pulses and that the effect of decreasing the film thickness from 50 to 25 nm was to reduce the amount of latent heat released upon the bulk nucleation of the solid phase throughout the whole molten volume. As a consequence, recalescence effects, i.e., a substantial reduction of the initial supercooling leading to a slowing down of the solidification process, 17,18 were minimized upon reduction of the film thickness, enabling the phase cyclability and reducing the solidification time to hundreds of ps. In contrast, studies performed on 50-nm-thick films under 100 fs pulses showed an a-to-c transformation time of ϳ30 ns.…”

Supercooling and structural relaxation in amorphous Ge films under pulsed laser irradiation

“…The final reflectivity value observed in this case is always lower than the initial one and Raman spectroscopy indicates the formation of polycrystalline material. 27 This type of transient has been reported earlier and has been related to recalescence and crystalline phase formation during solidification 28 as discussed elsewhere. 25 The transients obtained upon ps pulse irradiation of films on Si substrates are similar to the transient ͑a͒ in Fig.…”

On the origin of recalescence in amorphous Ge films melted with nanosecond laser pulses

“…These features are consistent with an increase of the liquid temperature produced by the the release of solidification enthalpy, and thus the occurrence of recalescence. [9][10][11]15 The reflectivity after the shoulder decreases again down to a final value that is always smaller than the initial one.…”

“…The dominant role of both the undercooling/supercooling degree prior to solidification and the presence of recalescence in the formation of either crystalline or amorphous phases is widely recognized. [9][10][11][12] It has been suggested that the films thickness is a key parameter controlling both the heat flow to the substrate 10 and the occurrence of recalescence 12 upon laserinduced melting of Si films on insulating substrates. These works deal however with Si films on substrates of very low thermal conductivity ͑mainly SiO 2 ͒ and film thicknesses much smaller than the thermal diffusion length of Si.…”