A Pathway to Type-I Band Alignment in Ge/Si Core-Shell Nanowires

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Germanium/Silicon core-shell nanowires (Ge/Si CSNWs) are promising for advanced electronic devices.
• Understanding their electronic band structure is crucial for device optimization.

Purpose of the Study:

• To investigate the electronic band structures of Ge/Si CSNWs.
• To engineer an electron quantum well within Ge core atoms.
• To explore band alignment transitions and their relation to quantum confinement and strain.

Main Methods:

• First-principles calculations were employed to analyze electronic band structures.
• Charge density and band structure analyses were performed.
• The effects of quantum confinement and lattice strain were systematically studied.

Main Results:

• Band engineering via quantum confinement and lattice strain induces a type-I/II band alignment transition.
• Type-I band alignment creates an electron quantum well in Ge/Si CSNWs.
• The type-I/II transition correlates with a direct-to-indirect band gap transition.
• Nanowire directionality ([100], [111], [110]) and diameter influence band alignment.
• Compressive strain on [110] CSNWs can achieve type-I band alignment.

Conclusions:

• Ge/Si CSNWs can be engineered to exhibit type-I band alignment.
• This capability allows for the fabrication of both n-type and p-type quantum-well transistors.
• The engineered Ge/Si CSNWs are suitable for high-speed logic applications.