Femtosecond and nanosecond pulsed laser deposition of silicon and germanium

Abstract

150fs Ti:Sapphire laser pulsed laser deposition of Si and Ge were compared to a nanosecond KrF laser (25ns). The ablation thresholds for ns lasers were about 2.5Jcm−2 for Si and 2.1Jcm−2 for Ge. The values were about 5–10 times lower when fs laser were used. The power densities were 108–109Wcm−2 for ns but 1012Wcm−2 for fs. By using an ion probe, the ions emission at different fluence were measured where the emitting ions achieving the velocity in the range of 7–40kms−1 and kinetic energy in the range of 30–200eV for ns laser. The ion produced by fs laser was measured to be highly energetic, 90–200kms−1, 2–10KeV. Two ion peaks were detected above specific laser fluence for both ns and fs laser ablation. Under fs laser ablation, the films were dominated by nano-sized crystalline particles, drastically different from nanosecond pulsed laser deposition where amorphous films were obtained. The ions characteristics and effects of pulse length on the properties of the deposited films were discussed.