Strain-conserving doping of a pseudomorphic metastable Ge_0.06Si_0.94 layer on Si(100) by low-dose BF⁺₂ implantation

A thick (260 nm) pseudomorphic metastable n-type Ge_0.06A_0.94 layer grown by molecular beam epitaxy on an n-type Si(100) substrate was implanted at room temperature with 70 keV BF⁺₂ ions to a dose of 3 × 10¹³ cm^-2, so that a p - n junction was formed in the GeSi layers. The samples were subsequently annealed for 10-40 s in a lamp furnace with a nitrogen ambient, or for 30 min in a vacuum-tube furnace. The samples were characterized by 2 MeV ⁴He backscattering/channeling spectrometry, double-crystal x-ray diffractometry, transmission electron microscopy, and by Hall effect measurements using the van der Pauw sample geometry. Samples annealed for either 40 s or 30 min at 800°C exhibit full electrical activation of the boron in the GeSi epilayer without losing their strain. The Hall mobility of the holes is lower than that of p-type Si doped under the same experimental conditions. These results can be attributed to the Hall factor of heavily doped p-type GeSi films which is less than unity while the Hall factor of a heavily doped p-type Si or n-type GeSi film is close to unity. When annealed at 900°C, the strain in both implanted and unimplanted layers is partly relaxed after 30 min, whereas it is not visibly relaxed after 40 s.