Effects of BF 2+ implantation on the strain-relaxation of pseudomorphic metastable Ge 0.06Si 0.94 alloy layers

Abstract

Metastable pseudomorphic Ge 0.06Si 0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF 2 + ions with three different doses of 3 × 10 13, 1 × 10 14, and 2.5 × 10 14 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 × 10 14 BF 2 + 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 × 10 13 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 800°C for 30 min after implantation to a dose of 2.5 × 10 14 cm −2. It is concluded that such a low dose of 3 × 10 13 BF 2 + 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.