Hexagonal germanium formation at room temperature using controlled penetration depth nano-indentation.

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Thin germanium (Ge) films on silicon (Si) substrates are crucial for semiconductor applications.
• Understanding the mechanical behavior and phase transformation of Ge films under stress is essential for device performance.

Purpose of the Study:

• To investigate the deformation mechanisms and phase transformations in Ge films on Si during low-load nano-indentation.
• To explore the influence of indentation depth and stress distribution on the resulting Ge phases.

Main Methods:

• Low-load nano-indentation using a Berkovich diamond tip on Ge films grown on Si.
• Ex-situ analysis of residual impressions using Raman Micro-Spectroscopy, Atomic Force Microscopy, and Transmission Electron Microscopy.

Main Results:

• Evidence of deformation by phase transformation at room temperature under critical pressures (4.9 GPa–8.1 GPa).
• Formation of new Ge phases (r8-Ge, hd-Ge, amorphous Ge) dependent on indentation depth.
• Inelastic deformation and fracture response are critically dependent on indentation penetration depth and shear stress distribution.

Conclusions:

• Nano-indentation can reliably induce phase transformations in Ge-on-Si films.
• Indentation depth and indenter geometry offer potential for tuning the contact response of Ge and other semiconductor thin films.
• This phenomenon has potential applications in creating narrow band gap materials for mid-wavelength infrared detection.