Investigation of Energy and Density of Laser-Ablated Si and Ge Plasma Ions Along With Surface Modifications

Abstract

The energy and density of laser-generated Si and Ge plasma ions have been investigated by using Faraday cup (FC). Nd: YAG laser (532 nm, 6 ns) at different irradiances ranging from 4 to 7.1 GWcm−2 has been employed as an irradiation source. FC measurements reveal two time-of-flight (TOF) ion signal peaks. From the observed TOF signals of ions, the kinetic energy and density of laser induced Si and Ge plasma ions have been evaluated. With increasing the laser irradiance from 4 to 7.1 GWcm−2, the Si ions density varies from $4.9\times 10^{20}$ cm−3 to $5.62\times 10^{20}$ cm−3, whereas for Ge ions, it varies from $11\times 10^{20}$ cm−3 to $12\times 10^{20}$ cm−3. Similarly, the evaluated values of Si ion energy range from 156 to 166 eV, whereas for Ge ion, energy varies from 108 to 124 eV. It was also revealed that both energy and density of plasma ions are strongly dependent on FC distance from the target surface as well as the angle of FC with respect to the target surface normal. By employing an electric probe, self-generated electric field (SGEF) of laser-induced plasmas of both Si and Ge has also been measured and it varies from 94 to 122 and 101 to 158 V/m, respectively, with increasing the laser irradiances from 4 to 6 GWcm−2. The observation of SGEF confirms the existence of double layer potential in laser-induced Si and Ge plasmas. Scanning electron microscope (SEM) analysis has been performed to establish a correlation between number density of the Si spikes and the periodicity of laser-induced periodic surface structure of Ge grown after ablation with evaluated corresponding ion density of Si and Ge plasmas. Surface structures grown on Si and Ge after laser ablation enhance their optical, electrical, and field emission properties to make them useful in solar cells, LED displays, electronic device, as well as for the fabrication of nanograting.