Buried superconducting films in Si containing Ga-rich precipitates

Recently a lot of research has been done in revealing the nature of intrinsic superconductivity in highly p-type doped silicon and germanium. However, the studies presented here, demonstrate the feasibility of embedding extrinsic superconducting nanolayers in commercial (100) silicon wafers due to Ga precipitation. With the ion implantation technique a high Ga fluence (2x10¹⁶ cm^-2 or 4x10¹⁶ cm^-2) is introduced in Si through a 30 nm SiO2 cover layer. This leads to amorphous layers containing Ga peak concentrations far beyond the equilibrium solid solubility limit. To initiate Ga precipitation and recrystallization rapid thermal annealing (RTA) is used. At optimized processing conditions (4x10¹⁶ cm^-2, 600 - 700°C) the samples become superconducting. Critical temperatures of 7 K and in plane critical fields up to 14 T are reached [1]. A detailed investigation of the layer microstructure by means of RBS/C and TEM will be presented. These structural investigations reveal polycrystalline Si layers containing amorphous Ga-rich precipitates and that the superconductivity arises because of a high density of precipitates at the Si/SiO2 interface. As the ion implantation with subsequent annealing is compatible with standard microelectronic technology it could be possible to develop new superconducting devices, which operate above liquid He temperature.
[1] Skrotzki R. et al., Appl. Phys. Lett. 97 (2010) 192505