Probing Intrawire, Interwire, and Diameter-Dependent Variations in Silicon Nanowire Surface Trap Density with Pump-Probe Microscopy
- Cating, Emma E. M. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Pinion, Christopher W. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Christesen, Joseph D. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Christie, Caleb A. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Grumstrup, Erik M. [ Montana State University: Chemistry & Biochemistry ] [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Cahoon, James F. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
- Papanikolas, John M. [ Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA ]
Surface trap density in silicon nanowires (NWs) plays a key role in the performance of many semiconductor NW-based devices. We use pump-probe microscopy to characterize the surface recombination dynamics on a point-by-point basis in 301 silicon NWs grown using the vapor-liquid-solid (VLS) method. The surface recombination velocity (S), a metric of the surface quality that is directly proportional to trap density, is determined by the relationship S = d/4 tau from measurements of the recombination lifetime (tau) and NW diameter (d) at distinct spatial locations in individual NWs. We find that S varies by as much as 2 orders of magnitude between NWs grown at the same time but varies only by a factor of 2 or three within an individual NW. Although we find that, as expected, smaller-diameter NWs exhibit shorter tau, we also find that smaller wires exhibit higher values of S; this indicates that tau is shorter both because of the geometrical effect of smaller d and because of a poorer quality surface. These results highlight the need to consider interwire heterogeneity as well as diameter-dependent surface effects when fabricating NW-based devices.