The Irradiance-Based Growth of Surface Structures Induced by Nanosecond Laser Pulses on Si and Ge and Their Correlation With Plasma Ion Kinetic Energies and Densities

Abstract

The laser irradiance-based surface structural growth on Si and Ge has been correlated first time with plasma parameters. The better control over plasma parameters makes manufacturing of various sized and shaped surface structures on the semiconducting materials. The effect of laser irradiances on surface morphology of Si and Ge has been explored. Nd: YAG laser (532 nm, 6 ns, 10 Hz) has been employed as an irradiation source at laser irradiances (4 -7.1 GW/cm2 ) under the vacuum condition. Surface modifications of laser ablated targets were analyzed by SEM analysis. It has been revealed that laser irradiance plays a significant role in the growth of the micro- and nanostructures on the laser irradiated target surfaces. The surface morphology of laser ablated Si and Ge exhibited the formation of Laser-Induced Periodic Surface Structures, cracks, spikes, ridges and cones. Density and size of these structures have been found to be strongly dependent upon the laser irradiances. Faraday cup has been employed in order to probe the kinetic energy and density of laser induced Si and Ge plasma ions at the similar values of laser irradiances. A correlation at similar values of laser irradiances has been established between the evaluated plasma ion parameters and observed structures for both materials. The results of ion energies are explained by the generation of ambipolar field or Self-Generated Electric Field in expanding plasma due to charge separation and double layer structure. The values of SGEF have also been evaluated at different laser irradiances.