Investigation of phase changes in Ge1Sb4Te7 films by single ultra-fast laser pulses

Abstract

The phase transformations induced in a Ge1Sb4Te7 system by a femtosecond (fs) laser exposure were investigated. The system has a multilayer structure of 15 nm ZnS–SiO2/80 nm Ge1Sb4Te7/100 nm ZnS–SiO2/0.6 mm polycarbonate substrate. The morphology and contrast of marks formed 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 fs shots. Phase-reversible transformations in the system have been achieved through careful adjustment of the laser fluence. The mechanism of reversibility triggered by fs laser pulses is discussed. The feasibility of phase-change reversible optical recording with the active Ge1Sb4Te7 layer using single fs pulses with a duration of 400 fs within well-defined fluence and pulse energy windows is therefore demonstrated. Our work also demonstrates that it is possible to record and retrieve data rapidly in the Ge1Sb4Te7 film within a conventional optical disk structure using non-amplified laser systems as laser sources.