The piezoresistance of silicon has been studied over the past few decades in order to characterize the material's unique electromechanical properties and investigate their wider applicability. While bulk and top-down (etched) micro-and nano-wires have been studied extensively, less work exists regarding bottom-up grown microwires. A facile method is presented for characterizing the piezoresistance of released, phosphorus-doped silicon microwires that have been grown, bottom-up, via a chemical vapour deposition, vapour-liquid-solid process. The method uses conductive tungsten probes to simultaneously make electrical measurements via direct ohmic contact and apply mechanical strain via bend deformation. These microwires display piezoresistive coefficients within an order of magnitude of those expected for bulk n-type silicon; however, they show an anomalous response at degenerate doping concentrations ($10 20 cm À3 ) when compared to lower doping concentrations ($10 17 cm À3 ), with a stronger piezoresistive coefficient exhibited for the more highly doped wires. This response is postulated to be due to the different growth mechanism of bottom-up microwires as compared to top-down. V C 2015 AIP Publishing LLC.
A wide variety of apparently contradictory piezoresistance (PZR) behaviors have been reported in p-type silicon nanowires (SiNW), from the usual positive bulk effect to anomalous (negative) PZR and giant PZR. The origin of such a range of diverse phenomena is unclear, and consequently so too is the importance of a number of parameters including SiNW type (top down or bottom up), stress concentration, electrostatic field effects, or surface chemistry. Here, we observe all these PZR behaviors in a single set of nominally p-type, ⟨110⟩ oriented, top-down SiNWs at uniaxial tensile stresses up to 0.5 MPa. Longitudinal π-coefficients varying from −800 × 10−11 Pa−1 to 3000 × 10−11 Pa−1 are measured. Micro-Raman spectroscopy on chemically treated nanowires reveals that stress concentration is the principal source of giant PZR. The sign and an excess PZR similar in magnitude to the bulk effect are related to the chemical treatment of the SiNW
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