Internal Structuring of Semiconductors with Ultrafast Lasers: Opening a Route to Three-Dimensional Silicon Photonics

Important challenges remain to achieve reliable three-dimensional laser writing inside semiconductors as important as silicon. Experiments show that nonlinear energy deposition with long infrared laser pulses can modify silicon internally. However, the level of controllability is extremely limited compared with the femtosecond laser nanostructuring regimes reported in transparent dielectrics. Recent efforts have concentrated on the specificities of the bulk silicon response to tightly focused ultrashort pulses. The strong propagation nonlinearities inherent to narrow band-gap semiconductors limit the space-time laser energy localization and prevent in most cases material breakdown with the shortest pulses. This chapter proposes an overview of this emerging topic and the practical solutions to this problem. It also discusses the potential of three-dimensional laser nanostructuring in narrow band-gap semiconductors to address applications in different fields. Among them, the first demonstrations of refractive index laser engineering in silicon open the perspective to move silicon photonics from two-dimensional systems to monolithic three-dimensional architectures.