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

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 [Herrmannsdörfer 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.

Electron Concentration Limit in Ge Doped by Ion Implantation and Flash Lamp Annealing

“…Moreover, the inset in Figure 3d shows that the diffusion of Sn can be fully suppressed using ms-range solid phase epitaxy. We have observed the same effect for other elements implanted into Ge, like Al, Ga, or P [6,7,25]. It is clear that, within the island, the Ge forms a continuous layer, but voids are well visible below the surface.…”

“…It has been shown that p-type doping in Ge is less problematic, while n-type doping remains challenging. Al or Ga that are implanted into Ge and subjected to rapid thermal annealing (RTA) for tens of seconds or flash lamp annealing (FLA) for milliseconds act as acceptors at hole concentrations above 10 21 cm −3 [4][5][6]. Such highly doped Ge exhibits superconductivity at critical temperatures below 1 K and it can provide excellent low resistive ohmic contacts.…”

“…Such highly doped Ge exhibits superconductivity at critical temperatures below 1 K and it can provide excellent low resistive ohmic contacts. In case of n-type doping, P ions are the most attractive due to the highest solubility limit among other group V elements and relatively low activation energy [6][7][8][9]. However, conventional doping using P implantation that is followed by RTA or furnace annealing is limited to the concentration of about 5 × 10 19 cm −3 .…”

Chlorine doping of MoSe2 flakes by ion implantation

“…33 Recently, we have shown that dopant diffusion in semiconductors can be significantly suppressed using strongly non-equilibrium thermal processing, e.g. ms-range FLA. [34][35][36] During FLA, the peak temperature is close to the melting point of the material to be annealed but never beyond. This ensures the recrystallization of the implanted layer via explosive solid phase epitaxy.…”

Observation of Distinct Superconducting Phases in Hyperdoped p-type Germanium

“…In its pure and alloyed state, Ge is used in a wide variety of roomtemperature electronics with high integrability with Si technology. Superconductivity in Ge is demonstrated through Ga + ion implantation followed by dopant activation via rapid thermal annealing (RTA) or flash lamp annealing (FLA) at temperatures near the Ge melting point (∼ 938 • C) 16,[21][22][23] . Such high temperatures were intended for recovering the crystallinity of the Ge substrate damaged by implantation.…”