Laser-Induced Crystallization of Ge/Sn Multilayer Amorphous Films

A comparative analysis of the structural, morphological, and optical properties of 150-nm-thick polycrystalline GeSn films formed by laser annealing of amorphous multilayer heterostructures on a Ge/Si(100) buffer layer using two types of radiation – pulsed nanosecond (λ = 355 nm) and femtosecond (λ = 800 nm) was carried out. According to Raman spectroscopy and X-ray diffraction data, pulsed nanosecond UV annealing within a narrow pulse energy density range of 0.2–0.3 J/cm² is most effective for preserving surface planarity and achieving maximum substitutional incorporation of tin (up to 10.3 at.% Sn). Femtosecond annealing provides a lower level of tin incorporation (7.5 at.%) due to intermixing of Sn and Ge elements at the interface between the film and the buffer layer, as confirmed by secondary ion mass spectrometry profiles. It is shown that the surface morphology of the films under these two types of laser processing also differs substantially; in particular, femtosecond annealing causes self-organization of laser-induced periodic surface structures (LIPSS), which are promising for application in specialized optoelectronic devices.