Silicon nanowire piezoresistance: Impact of surface crystallographic orientation

We investigate piezoresistance in lithographically defined silicon nanowires of various cross-sectional aspect ratios. Both 〈 110 〉 - and 〈 100 〉 -oriented nanowires are investigated under 〈 110 〉 -oriented strain. The nanowire thickness is varied from 23 to 45 nm and the nanowire width is varied from 5 to 113 nm. Our data shows piezoresistance in silicon nanowires being a surface induced effect with {110} surfaces inducing a much larger piezoresistance than {100} surfaces. This is consistent with a higher density of surface states on {110} surfaces than on {100} surfaces. Our experimental findings support recent computational work pointing toward surface states being the source of giant piezoresistance in silicon nanowires.