Deep surface amorphization in silicon induced by spectrally-tuned ultrashort laser pulses

Irradiation of crystalline silicon with ultrashort laser pulses is a well-known method for creating thin amorphous surface layers. The underlying mechanisms are based on ultrafast melting and rapid quenching of the molten phase, preventing the formation of the crystalline phase. The interest of this method for applications in the electronics industry lies in the very different electrical properties of the amorphous phase obtained. It has also triggered strong attention in the field of silicon photonics, the amorphous phase exhibiting a higher refractive index than the crystalline phase at telecom wavelengths. This simple feature could be exploited for low-loss optical waveguiding in a thin amorphous surface layer, provided the latter is sufficiently thick. However, the maximum thickness of laser-induced amorphous layers reported to date is < 70 nm [1] , which is below the requirements for supporting guided modes.