Effects of BF⁺₂ implantation on the strain-relaxation of pseudomorphic metastable Ge_0.06Si_0.94 alloy layers

Metastable pseudomorphic Ge_0.06Si_0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (100) substrates were implanted at room temperature by 70 keV BF₂⁺ ions with three different doses of 3×10¹³, 1×10¹⁴, and 2.5×10¹⁴ cm^-2. The implanted samples were subsequently annealed at 800 °C and 900 °C for 30 min in a vacuum tube furnace. Observed by MeV ⁴He channeling spectrometry, the sample implanted at a dose of 2.5×10¹⁴ BF₂⁺ cm^-2 is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge_0.06Si_0.94 samples become pronounced as the dose increases. Only the samples implanted at 3×10¹³ cm^-2 do not visibly degrade nor relax during anneal at 800 °C. In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 8000 °C for 30 min after implantation to a dose of 2.5×10¹⁴ cm^-2. It is concluded that such a low dose of 3×10¹³ BF₂⁺ cm^-2 can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900 °C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.