Superconductivity in single-crystalline, aluminum- and gallium-hyperdoped germanium

TL;DR

This study demonstrates the successful creation of single-crystalline, hyperdoped germanium with aluminum and gallium, exhibiting phonon-mediated superconductivity at low temperatures, with experimental and theoretical analysis confirming the phenomenon.

Contribution

It reports the first synthesis of superconducting single-crystalline Ge hyperdoped with Al and Ga via ion implantation and flash lamp annealing, with theoretical support for phonon-mediated superconductivity.

Findings

Superconductivity observed in single-crystalline Ge hyperdoped with Al and Ga.

Critical temperature around 0.45 K for 6.25 at.% dopant concentration.

Doping levels exceed equilibrium solubility by eight times.

Abstract

Superconductivity in group IV semiconductors is desired for hybrid devices combining both semiconducting and superconducting properties. Following boron doped diamond and Si, superconductivity has been observed in gallium doped Ge, however the obtained specimen is in polycrystalline form [Herrmannsd\"orfer et al., Phys. Rev. Lett. 102, 217003 (2009)]. Here, we present superconducting single-crystalline Ge hyperdoped with gallium or aluminium by ion implantation and rear-side flash lamp annealing. The maximum concentration of Al and Ga incorporated into substitutional positions in Ge is eight times higher than the equilibrium solid solubility. This corresponds to a hole concentration above 10^21 cm-3. Using density functional theory in the local density approximation and pseudopotential plane-wave approach, we show that the superconductivity in p-type Ge is phonon-mediated. According to the ab initio calculations the critical superconducting temperature for Al- and Ga-doped Ge is in the range of 0.45 K for 6.25 at.% of dopant concentration being in a qualitative agreement with experimentally obtained values.