Description
Cadmium telluride (CdTe), lead sulfide (PbS), and indium tin oxide (ITO) are semiconductor materials commonly used in photovoltaic technologies, light-emitting diodes, and radiation detectors for Free Electron Laser sources. Ultrafast XUV/X-ray irradiation of these materials was modelled with the state-of-the-art hybrid code XTANT-31,2. ITO and PbS disorder at ∼0.3-0.4 eV/atom and ∼0.2-0.3 eV/atom, respectively, while CdTe transiently disorders at irradiation doses above ∼0.4-0.5 eV per atom; therefore, being more resistant to ultrafast irradiation, comparable to CdS3 but with slower phase transition dynamics. At the threshold doses, the melting induced is primarily thermal, triggered by electron–phonon coupling, which heats the atomic system. All the materials also exhibit nonthermal melting at higher doses: CdTe at 0.8 eV/atom, PbS at 0.9 eV/atom, and ITO at 1 eV/atom. CdTe and PbS may transiently form semiconducting melted states in the dose intervals between 0.5 and 0.7 eV/atom while turning into metallic liquid at higher doses. CdTe and ITO exhibit simultaneous solid and liquid sublattices, which is characteristic of transient superionic states. The threshold doses increase if energy sinks from the samples and corresponding recrystallization are taken into account. CdTe appears to have the highest recrystallization degree among the studied materials. Simulations with a thermostat (characteristic cooling time of 1 ps) show that below the threshold dose of 1.5 eV/atom, the band gap of each material returns to its original value. With the increase of the dose, the cooled state becomes more amorphous, with correspondingly smaller band gap until an equilibrium value is reached. The results suggest that femtosecond lasers may be useful in tuning the band gap of photovoltaic semiconductors. Material ablation from the surface occurs at deposited doses of 0.6 eV/atom in CdTe and 0.4 eV/atom in PbS and ITO, emitting Te, S, and O, respectively, at timescales of ~10 ps.
