Synthesis of Si/Si_1-xGe_x/Si heterostructures for device applications using Ge⁺ implantation into silicon

The synthesis and doping of Si/Si_1-xGe_x/Si heterostructures by ion implantation is being investigated as an alternative to epitaxial deposition as a means of forming heterostructures for device applications. Test structures with graded Si/Si_1-xGe_x/Si interfaces have been formed in n-type Si wafers by the implantation of 70 keV or 140 keV Ge⁺ ions and doses up to 3×10¹⁶ Ge⁺ cm^-2 to form alloy layers with peak Ge concentrations of up to 11 atomic%. BF₂⁺ ions have been implanted to form p-type surface layers and post amorphisation, using 500 keV Si⁺ into cooled substrates followed by solid phase epitaxial regrowth, has been used to control End of Range (EoR) defects. TEM data from post amorphised samples reveal no extended defects within the alloy region but show a band of EoR defects buried 1 μm beneath the surface. The composition, microstructure and junction quality of the alloy layers are discussed to highlight the potential impact of the process on the manufacturability of advanced bipolar (HBT) devices