Phase transformations induced in Ge₁Sb₂Te₄ films by single femtosecond pulses

We have investigated the phase transformations induced in a Ge₁Sb₂Te₄ system by a femtosecond laser exposure. The system has a multilayer structure of 10 nm ZnS-SiO₂/(10-100 nm) Ge₁Sb₂Te₄/80 nm ZnS-SiO₂/0.6 mm polycarbonate substrate. The morphology and contrast of marks written in both amorphous and crystalline backgrounds by single fs pulses were characterized using an optical microscope. X-ray diffraction was applied to identify the crystal structures formed by single 108 fs shots. The characteristics and the conditions of crystalline → amorphous or amorphous → crystalline transitions in the multilayer structures with different Ge₁Sb₂Te₄ layer thickness triggered by single shots were investigated. The pulse energy window for the crystallization or amorphization in the Ge₁Sb₂Te₄ systems was established. The mechanism of phase changes triggered by femtosecond laser pulses is discussed.