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

Abstract

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.

Explosive Crystallization Characteristic of Ge–Cu–Te Thin Films for Phase-Change Memory

“…Therefore, it is generally accepted that the EC of amorphous semiconductor thin films appears through an intermediately liquid layer in which melting takes place in a thin layer before the advancing crystallization front. Similar to Ge and Si thin films, it is tetrahedrally coordinated Ge–Cu–Te thin films that are beneficial for evolutions from a low-density amorphous (LDA) state to a high-density amorphous (HDA) state, which serves to produce an intermediately liquid layer . This is considered one of the intrinsic structural superiorities of Ge–Cu–Te thin films for EC.…”

“…Similar to Ge and Si thin films, it is tetrahedrally coordinated Ge−Cu−Te thin films 40 that are beneficial for evolutions from a low-density amorphous (LDA) state to a high-density amorphous (HDA) state, which serves to produce an intermediately liquid layer. 41 This is considered one of the intrinsic structural superiorities of Ge−Cu−Te thin films for EC. Additionally, clusters with a medium-range order (MRO) in a continuous random network (CRN) matrix of sputter-deposited pristine thin films may serve as nuclei and grow promptly by the liquid-like interface's mobility, leading to EC.…”

Effects of hydrogen on structure and crystallization behavior of sputter-deposited amorphous germanium films

“…12) Most recently, the formation of planar defects is attributed to the rapid formation of CPs, so-called explosive crystallization, which occurs in not stabilized films but pristine films. 13) These are unique properties of sputter-deposited pure a-Ge we have found up to now.…”

“…The partial pressure of Ar was fixed to be 0.7 Pa according to a series of our previous studies. [10][11][12][13] The partial pressure of H 2 was set between 0 and 0.55 Pa by referring to a report by Heya et al, 20) who prepared amorphous Si films with various hydrogen concentration by sputtering under the conditions of several ratios of H 2 and Ar pressures.…”

Impact of supercooled liquid structures on the crystallization processes of amorphous Ge

“…Low-energy electron irradiation into amorphous Ge also induces microstructures similar to explosive crystallization. 16,17) In this case, the crystallization occurred athermally due to electronic excitation effects and the temperature rise was negligible. This means that the mechanism of explosive crystallization is still a matter of debate.…”