Superconductivity in substitutional Ga-hyperdoped Ge epitaxial thin films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Quantum Technologies

Background:

• Doping group-IV elements like germanium (Ge) can induce superconductivity, but its origin is often unclear due to structural disorder.
• Achieving superconductivity in semiconductors is key for integrating quantum functionalities with existing semiconductor technologies.

Purpose of the Study:

• To investigate the epitaxial growth of hyperdoped gallium (Ga):Ge films and heterostructures.
• To understand the mechanism behind doping-induced superconductivity in group-IV elements.
• To establish a low-disorder superconductor-semiconductor platform.

Main Methods:

• Epitaxial growth of hyperdoped Ga:Ge films and trilayer heterostructures using molecular-beam epitaxy.
• Characterization using synchrotron-based X-ray absorption and scattering.
• First-principles calculations to corroborate experimental findings.

Main Results:

• Achieved extreme hole concentrations (4.15 × 10^21 cm^-3) with 17.9% Ga substitution in Ge.
• Observed superconductivity with a critical temperature (Tc) of 3.5 K.
• Revealed substitutional incorporation of Ga atoms, causing tetragonal distortion and suggesting a narrow band formation.

Conclusions:

• The structural order of Ga dopants in Ge is crucial for the emergence of superconductivity.
• Hyperdoped Ga:Ge serves as a low-disorder, epitaxial superconductor-semiconductor platform.
• This work enables the development of quantum functionalities in accessible material systems.