Observations on crystalline transformation in amorphous Ge thin films

The crystalline transformation of amorphous Ge films as a function of film thickness and environment has been studied using electron diffraction, electron microscope and electron microprobe techniques. Crystallization heat treatments were carried out in an electron diffraction unit on two series of films, one examined immediately following deposition and the other after being exposed to air at room temperature for several weeks. It was found in both series that crystallization is independent of film thickness. The transformation occurred at 375° ± 10°C over a broad range of thicknesses from 40 Å to 260 Å. On heating the films to 700°C, however, a difference in structure between the two film series was observed. Films exposed to air showed the formation of GeO2 in addition to Ge. This difference, analyzed by transmission electron microscopy and the electron microprobe, could be attributed to a surface oxide and suggests that surface contamination does occur on aging at room temperature but does not alter the crystalline transformation of the amorphous material. © 1972.