Transmissivity to reflectivity change delay phenomenon observed in GeTe thin films at laser-induced reamorphization

• Laser-induced phase transition of GeTe thin film coating. • High optical properties contrast for two stable laser-induced phase states. • Transmissivity to reflectivity delay observed during reamorphisation process. • Thin film temperature kinetics’ computational model. The article presents the results of an in-situ pump–probe study of the change’s kinetics in the optical properties of GeTe thin films associated with reversible phase transitions initiated by nanosecond laser pulses. It was shown that the change of the transmissivity and reflectivity of GeTe films in case of direct phase transition from the amorphous state to the crystalline starts at the same time, while the reverse transition is observed delay change of the transmissivity relative to the reflectivity. The value of this delay for the 100 nm GeTe thin film was estimated at t 100 = 24 ns, and for the 50 nm sample – t 50 = 13 ns. This time lag in changes of the transmissivity from the reflectivity in case of reamorphization films depending on sample thickness, can be explained by the high contrast of the concentration of free electrons between amorphous and crystalline states, which determine the reflectivity of the surface layer of the sample, while the transmissivity is determined by the total thickness. The experimental dependences of the kinetics of changes in the optical properties of GeTe samples under laser-induced phase transitions are in good consistent with the numerical simulation data of the Stefan problem.