Diffusion of Ge below the Si(100) surface: theory and experiment

Area of Science:

• Materials Science
• Surface Science
• Solid-State Physics

Background:

• Understanding the diffusion of germanium (Ge) into silicon (Si) is crucial for fabricating advanced semiconductor devices.
• Subsurface diffusion of Ge in Si(100) influences the properties of Si/Ge heterostructures.

Purpose of the Study:

• To investigate the diffusion of Ge into the subsurface layers of Si(100).
• To determine the equilibrium Ge subsurface distributions and the energy pathways involved.
• To explore the effect of doping on Ge diffusion and Si/Ge interface sharpness.

Main Methods:

• Experimental measurements using Auger electron diffraction.
• Theoretical predictions employing density functional theory (DFT).

Main Results:

• Germanium was observed in the fourth layer of Si(100) after submonolayer growth at temperatures as low as 500°C.
• DFT predictions of equilibrium Ge subsurface distributions align with experimental findings.
• A low energy pathway for Ge diffusion was identified, attributed to low interstitial formation energy in deeper Si layers.

Conclusions:

• Ge diffusion into subsurface Si layers occurs readily, even at moderate temperatures.
• The formation energy of Ge interstitials is significantly influenced by doping.
• N-type doping shows potential for creating sharper Si/Ge interfaces due to altered formation energies.