Formation of periodic strained layers associated with nanovoids inside a silicon carbide single crystal induced by femtosecond laser irradiation

Abstract

We observed the formation of subwavelength periodic strained layers associated with nanovoids in the cross section of femtosecond laser-irradiated lines written inside 4H-SiC single crystals. Both conventional and high-voltage transmission electron microscopies were carried out for microstructural analyses. The cross section of the irradiated lines consists of four to six groups of fine periodic structures. Each group is composed of strained layers with a typical spacing of 150 or 300 nm. The layers extend along the irradiated lines, aligned parallel to the electric field of the laser light. Tiny voids approximately 20 nm in diameter are found in the layers.

Tailoring thermoelectric properties of nanostructured crystal silicon fabricated by infrared femtosecond laser direct writing

“…g and h). Another group has also observed that the formation of periodic strained layers associated with nanovoids inside a SiC single crystal . Since a SiC is an indirect band gap semiconductor, their results are consistent with our interpretation that the nanostructures can be formed inside a material only if it is an indirect bandgap semiconductor.…”

Femtosecond laser-induced self-ordered nanostructures in semiconducting 4H-SiC

“…in good agreement with experimental results[4]. (The value s k depends on excess nonequilibrium electrons concentration on the critical one and on refractive index of semiconductor.)…”

“…Back wave, that go toward the laser radiation and is needed for interference, is created due to reflection by system of formed temporary and remnant regular nanostructures. Since plasma channel is surrounded by semiconductor matter, the period of resulting nanostructures is In experiments [4] the array of laser beam multifilamentation was observed along laser beam track in semiconducting 4H-SiC due to excess laser beam intensity, see fig.1a,b, similar as for gases [12] and dielectrics [13]. The later nonlinear effect includes the process of nonequilibrium solidstate plasma formation..…”

“…The resonance ordering of may be due to their displacement by electric field of standing interference picture of electromagnetic waves (SPP and incident laser wave interference). The possible course of decreasing of small-scale nanostructure formation threshold, that was discovered in [4], is increasing the efficient converting of falling laser radiation in SPP waves inside material, where it is higher than around surface, at localization field's maximum of SPP where they faster decay due to scattering on defects.…”

“…Note, that regular structures on 4 -SiC include the regular sequence of nanovoids with character diameter 10 nm [4]. Nanovoids with typical size about a part of microns was observed along tracks in glass [11], and also in resonance periodical structures that form in glass volume (nanocracks having wide about 10 nm [14]) after irradiation by many pulses of femtosecond radiation.…”