Paper NS+AS+EM-MoA8
Geometry-Dependent Formation of Multiple Twins in Si Nanowires

Monday, October 28, 2013, 4:20 pm, Room 203 B

Precise control of twin boundaries and stacking faults in semiconductor nanowires provides a number of exciting opportunities to fundamentally manipulate their optical, electrical, and thermal properties. Group IV nanowires, as opposed to their III-V counterparts, rarely exhibit planar defects perpendicular to the {111} orientation and rationally engineering their insertion remains challenging. Here we extend our recent demonstration of defect introduction in vapor-liquid-solid (VLS) synthesized, {111} oriented Si nanowires¹ and report on the appearance of consecutive, geometry-dependent twin boundaries for the first time. Si nanowires with double twins were grown with a Au catalyst by initiating growth at T = 490 ^oC and P = 2×10^-4 Torr for 10 min before changing to T = 410 ^oC and P = 5×10^-4 Torr for another 10 min. While the position of the first twin boundary (TB₁) corresponds to the point where growth conditions were changed, and was the same for all nanowires, the second twin boundary (TB₂) exhibits a diameter-dependent axial position. Detailed electron microscopy analysis shows that thin {111} sidewall facets, which elongate following TB₁ and deform the triple-phase line, are responsible for the formation of TB₂. We hypothesize that an increased amount of surface hydrogen, present as a result of the condition change, favors the thin {111} facets. Our findings help to elucidate the mechanisms that underlie defect introduction in semiconductor nanowires and represent an important step toward the creation of complex defect superstructures in Si.

(1) Shin, N.; Chi, M.; Howe, J. Y.; Filler, M. A. Nano Lett., 2013, in press