Instabilities of Crystallization in Amorphous Germanium Under Pulsed Laser Irradiation

Abstract

Several crystallization mechanisms of amorphous solids under laser irradiation have been proposed in the last few years. In previous work, an explosive crystallization mechanism of thin amorphous germanium films under pulsed laser irradiation in a transmission electron microscope has been reported [1,2]. It was shown that a solid phase crystallization mechanism occurs at the crystallization threshold. Different results strongly depending on the crystallization conditions have been obtained on a-Ge by several workers. For example, pulsed laser and pulsed electron beam crystallizations may give similar [3,4] results or may not [5,6]; thermal crystallization [7,8] is different from laser recrystallization. We have also noted in our series of experiments that the morphological features of the crystallized pattern are very dependent on the thermal “prehistory” of the film. In order to gain further insight on the structural properties and the growth kinetics, we undertook a systematically controlled study where we examined the crystallization mechanism as a function of controlled parameters. We investigated the influence of the thickness of the films, the evaporation rate, repetitive laser pulses, as well as thermal preannealing of the film. We also calculated the maximal temperature reached in the film in the different regimes of crystallization observed.