Crystallization of sputter-deposited amorphous Ge films: Competition of diamond cubic and hexagonal phases

Ryusuke Nakamura ¹ Masayuki Okugawa ¹ Manabu Ishimaru ² Hidehiro Yasuda ³ Hiroshi Numakura ¹

¹Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Japan
²Department of Materials Science and Engineering, Kyushu Institute of Technology, Japan
³Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Japan

A fundamental understanding of the crystallization process of amorphous silicon (a-Si) and germanium (a-Ge) is relevant to the synthesis of a variety of technologically important thin-film devices used in electronic and opto-electronic industries such as solar cells, thin film transistors, etc. It is assumed that crystallization behavior depends largely on the initial amorphous structure. From both scientific and technological perspectives, to clarify progressive changes from prepared amorphous structures to crystalline phases is required.

In the present study, we have studied the effect of aging at room temperature [1] and heat treatment [2] on the amorphous structure and crystallization behavior of sputter-deposited a-Ge films. We report crystallization microstructure and crystal structures vary according to changes in the amorphous structure: the competition of coarse particles of a metastable hexagonal structure and fine nanograins of the stable diamond cubic structure. We discuss the relationship between the instability of medium-range ordered (MRO) clusters and the crystallization behavior.

[1] M. Okugawa, R. Nakamura, et al., J. Appl. Phys., 119, 214309 (2016).

[2] M. Okugawa, R. Nakamura, et al., AIP Advances, 6, 125035 (2016).