Effect of low Ge content on B diffusion in amorphous SiGe alloys

Diffusion of B in amorphous Si is known to be four orders of magnitude higher than in crystalline Si. The effect of Ge at low concentrations on B diffusion in the amorphous phase is unknown. 1.5 μm thick relaxed layers of varying SiGe alloys (0, 6, 12, and 100 at. % Ge) were grown on Si. After growth the layer was amorphized to a depth of 0.8 μm using a 500 keV, 5× 1015 ion cm2 Si+ implant at 77 K. Next a 500 eV, 1× 1015 ions cm2 B+ implant was introduced. The amorphous SiGe was recrystallized at temperatures between 300 and 600 °C and the B diffusion during solid phase epitaxial regrowth was studied using dynamic secondary ion mass spectrometry. Comparison of B diffusivities for amorphous Si and amorphous Si0.88 Ge0.12 revealed similar activation energies (2.7 and 2.8 eV, respectively) and preexponential factors (0.8 and 4.8 cm2 s, respectively). The negligible change in B diffusion in amorphous SiGe at low Ge concentrations is similar to reports on B diffusivity for strain-relaxed crystalline SiGe alloys with Ge content. These results suggest that Ge is not an effective trap for B in the amorphous phase.