The relation between amorphous structure and explosive crystallization of sputter-deposited amorphous germanium thin films

In amorphous germanium (a-Ge) and amorphous silicon films, extremely rapid crystallization, called explosive crystallization, is known to occur by instantaneous processes such as mechanical stimulation, laser irradiation, and electron irradiation. In the present study, using transmission electron microscopy, we have investigated crystallization of a-Ge induced by electron irradiation and flash-lamp annealing (FLA). We have found that the mode of crystallization depends on the amorphous state: explosive crystallization occurred by both electron irradiation and FLA in pristine films, while it did not occur in those aged at room temperature for over 6 months. In a previous paper [Okugawa et al., J. Appl. Phys. 119, 214309 (2016)], it was reported that liquid-like high-density amorphous (HDA) regions were formed in a-Ge films by the long-term aging. The explosive crystallization observed in pristine a-Ge films is suggested to occur via liquid-like HDA interfaces at the growth front. (C) 2019 The Japan Society of Applied Physics