UC Berkeley

Silicon nanostructures serve as the backbone of modern electronics and photonics. Particularly, silicon nanoresonator became an increasingly important building block for the advanced photonics applications, including sensing, wavefront engineering and integrated photonics. Its crystallinity engineering is critical for enabling the manufacturability as well as fueling the continuous innovation on the device functionalities. Meanwhile, the scalable patterning of such nanostructures could offer cost-effective and highly controllable manufacturing routes beyond the conventional complementary metal-oxide-semiconductor (CMOS) fabrication. Owing to the controllable energy delivery and capability to interact with nanostructures, pulsed laser processing could significantly shed light on the above challenges and opportunities.

The pulsed laser processing of semiconductor material has been intensely investigated in the last century providing insights into fundamental light-material interaction. In early this century, thin-film laser processing became the main research topic as the complex coupling of heat transfer and phase transformation has enabled the technical innovation towards thin-film transistors in the display industry. However, when the lateral dimensions of the semiconductor material further shrunk down to the order of 100nm, the governing laws of the multiphysics interaction had to incite a significant paradigm shift in the study of the optical coupling, heat transfer and phase transformations.

This dissertation focus on understanding new coupling mechanism of pulsed laser interaction with silicon nanostructures, and exploiting them for scalable patterning and crystal engineering of the functional resonator arrays. Based on the unique near-field enhanced optical absorption, we first demonstrate the optically directed assembly of silicon nanoresonators. Spherical silicon nanoresonators can be fabricated with programmable numbers and combinations. Based on the ultrafast quenching rate and high adhesion work of silicon, we then demonstrate the deformation-free reversible phase transformation of silicon resonators that enables the active modulation of visible wavelength metasurfaces. Our in situ reflection probing of a single silicon nanodisk coupled with comprehensive simulations helps to reveal the mechanism behind the amorphization. We believe the experimental probing results lends support to the hypotheses silicon relaxation time scale on the silicon glass transformation. Lastly, through femtosecond laser irradiation, we observed the ultrafast field enhanced selective material removal within nanodisks. The detailed dynamics of the field enhancement, carrier excitation, non-thermal melting and subsequent cold ablation are studied ex-situ and in-situ. The mechanism can be used for scalable manufacturing of bowtie sensing structures and laser printing optical metasurfaces.