Crystallization of amorphous germanium in an Al/a-Ge bilayer film deposited on a SiO2 substrate

Abstract

The crystallization of amorphous Ge(a-Ge) in an Al (134 nm) and a-Ge (108 nm) thin-film bilayer deposited on a SiO2 substrate has been examined by a cross section transmission electron microscope technique. When crystallization of a-Ge begins at 125 °C, amorphous AlGe (a-AlGe) alloy is formed in the Ge layer. Then, the a-AlGe alloy layer also appeared at the surface of the bilayer. After complete crystallization, those amorphous layers disappeared and the bilayer film has been converted to a polycrystalline film. We discussed the crystallization of a-Ge and proposed the mechanism of the diffusion of Ge atoms from the inner a-Ge layer through the outer Al layer to the topmost surface that involves the formation of the metastable a-AlGe alloy in the Ge layer, followed by the crystallization of this alloy by the pseudo-eutectic reaction, leading to the decomposition into an equilibrium Al and Ge crystal mixture and a-Ge. Then, Ge atoms is released to the Al layer for the compensation of the Al diffusion down into the Ge layer and again forms the a-AlGe alloy in the Al layer. The a-AlGe alloy in the Al layer is also crystallized by the pseudo-eutectic reaction. Consequently, decomposed a-Ge is ejected from the inside to the surface of the bilayer, resulting in the surface Ge segregation.

Annealing Effects on Structures and Morphologies of Fe/Si Core–Shell Clusters

“…28,29) Anomalous metal-mediated crystallizations by low temperature annealing were also observed in amorphous semiconductor/metal double-layered films, and ascribed to very fast grain boundary diffusion of Si (or Ge) atoms through metal layers. 30,31) Since both Fe and Si diffusivities are small and their values for Fe are much smaller than that for Si in the bulk B20-type ordered FeSi alloy, 32) the insufficient annealing procedures (the short period and low temperature) may hinder the growth of the ordered FeSi and FeSi 2 phases in the present Fe/Si hybrid clusters.…”

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

“…The origin of the difference has been discussed in terms of film thickness 21,22 and impurities. 19,23 The present study revealed that crystallization temperature of a-Ge films, of the fixed thickness of 40 nm, varies from 500 • C to 600 • C depending on thermal history, with corresponding variations in the amorphous structure and the crystallization behavior from coarse particles with a hexagonal structure to homogeneous nanograins of the diamond cubic structure.…”

“…The values reported in the literature are grouped into two: low-temperature and high-temperature crystallization that occur at 400-500 • C [17][18][19] and at 600-650 • C, 20 respectively. The origin of the difference has been discussed in terms of film thickness 21,22 and impurities.…”

Elucidating the Metal-Induced Crystallization and Diffusion Behavior of Al/a-Ge Thin Films

“…5,6 Metal-induced crystallization (MIC) may occur in hermetic films during MEMS packaging. [7][8][9][10] In MIC, metal induces crystallization of semiconductor at a low temperature. The driving force for MIC is the difference between the free energies of the crystallized phase and the amorphous phase.…”