Optical and Thermal Behavior of Germanium Thin Films under Femtosecond Laser Irradiation

Abstract

In this study, we theoretically investigate the response of a germanium thin film under femtosecond pulsed laser irradiation. Electron and lattice temperatures, as well as material-specific optical properties such as dielectric function and reflectivity, were calculated during the irradiation using an extended two-temperature model coupled with the carrier density rate equation and the Drude model. Melting and ablation fluence thresholds were also predicted, resulting in 0.14 J cm−2 and 0.35 J cm−2, respectively. An ultrafast change in both optical and thermal properties was detected upon laser irradiation. Results also indicate that thermal melting occurs after germanium takes on a metallic character during irradiation, and that the impact ionization process may have a critical role in the laser-induced thermal effect. Therefore, we suggest that the origin of the thermal modification of germanium surface under femtosecond laser irradiation is mostly due the impact ionization process and that its effect becomes more important when increasing the laser fluence.

Wide-Spectrum Antireflective Properties of Germanium by Femtosecond Laser Raster-Type In Situ Repetitive Direct Writing Technique

“…Compared with other semiconductor materials such as Si and GaAs, Ge has a low coefficient of expansion, high temperature and pressure resistance, chemical stability, and high overload resistance. Ge also has good semiconductor industrial compatibility, as well as good narrow band gap and infrared transmission [3][4][5]. Thus, Ge is widely used in micro-and nano-device fabrication and related industry fields [6,7].…”