Periodic Surface Modification by Femtosecond Laser Irradiation on Semiconductors

This thesis focuses on the formation of laser induced periodic surface structures (LIPSS) on semiconductors by ultrafast laser irradiation, specifically on the observation of distinct LIPSS mechanisms and the modeling of its formation dynamics. In order to do so, experiments under various irradiation conditions and material systems were performed, and the subsequent material transformations were characterized using combinations of microscopy and chemical analysis techniques. Finally, the modeling of the irradiation dynamics is done both analytically and using finite element calculations. The first part of the study discusses the direct involvement of surface plasmon polaritons (SPP) and its interference with the laser field in the early stage of low spatial frequency LIPSS (LSFL) formation. In semiconductors, the SPP mode is supported by a brief metallic state transition during an ultrafast laser pulse irradiation. We further show that the transient dynamics strongly relate to the final characteristics of LSFL being formed. The second part of the study dwells more into the control of LSFL formation using plasmonic microstructures. Initialization of SPP field using a strong plasmonic coupler such as gold yields high intensity LSFL formations, which is consistent with the SPP-laser interference mechanism. LSFL intensity and orientation is also shown to be related to the geometry of the microstructures. Further, a variety of 2D periodic surfaces were created using the interference of multiple SPP sources. Finally, near field diffraction is shown to be a dominating mechanism of LSFL formation in the case where SPP coupling is negligible. The third part of the study analyzes a possible universal mechanism for high spatial frequency LIPSS (HSFL) formation involving point defect generation, diffusion, and accumulation in low band-gap semiconductors. We will examine the effect of laser frequency on possible point defect generation in silicon. Subsequently, we report periodic nanoscale island formation on Silicon previously observed only in compound semiconductors. Island formation is proposed to be the precursor for the subsequent HSFL evolution via light scattering in the near field. All of the studies outlined above achieve the common goal of highlighting the coupled interplay between optically driven surface modification mechanisms with a dynamically changing material structure and properties under transient strong electromagnetic field. The entirety of which, results in a variety of characteristic periodic modulations on semiconductor surfaces we have come to observe.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138571/1/ricobasc_1.pd