Thickness-dependent phase transformation in nanoindented germanium thin films

Area of Science:

• Materials Science
• Solid Mechanics
• Nanotechnology

Background:

• Epitaxial germanium (Ge) films on silicon (Si) substrates are crucial in semiconductor technology.
• Understanding their mechanical properties under stress is essential for device fabrication and reliability.

Purpose of the Study:

• To investigate the mechanical response and deformation mechanisms of epitaxial Ge films with varying thicknesses under nanoindentation.
• To explore the influence of film thickness and indenter geometry on the stress state and fracture behavior.

Main Methods:

• Nanoindentation experiments were performed on Ge films (50-600 nm) using a spherical diamond tip (R≈4.3 µm).
• Inelastic deformation mechanisms were analyzed based on load-displacement curves and post-indentation analysis.
• Elastic stress modeling was employed to correlate stress distribution with film thickness and indenter radius.

Main Results:

• The primary inelastic deformation mechanism in Ge films is critically dependent on film thickness.
• Sub-100 nm Ge films exhibit pressure-induced phase transformation, while thicker films deform via shear-induced dislocation slip and twinning.
• Nanoindentation fracture response also shows a strong dependence on film thickness.

Conclusions:

• Film thickness is a critical parameter controlling the mechanical response and deformation mechanisms of epitaxial Ge films.
• Varying film thickness and indenter radius offers a method to tailor the contact response of Ge and related thin film materials.
• This research provides insights for optimizing the mechanical properties of Ge thin films in microelectronic applications.