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Register a new userOn giant piezoresistance effects in silicon nanowires and microwires
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The giant piezoresistance (PZR) previously reported in silicon nanowires is experimentally investigated in a large number of surface depleted silicon nano- and micro-structures. The resistance is shown to vary strongly with time due to electron and hole trapping at the sample surfaces. Importantly, this time varying resistance manifests itself as an apparent giant PZR identical to that reported elsewhere. By modulating the applied stress in time, the true PZR of the structures is found to be comparable with that of bulk silicon.
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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, $langle 110 rangle$ oriented, top-down SiNWs at uniaxial tensile stresses up to 0.5 MPa. Longitudinal $pi$-coefficients varying from $-800times10^{-11}$ Pa$^{-1}$ to $3000times10^{-11}$ 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.
Piezoresistance is the change in the electrical resistance, or more specifically the resistivity, of a solid induced by an applied mechanical stress. The origin of this effect in bulk, crystalline materials like Silicon, is principally a change in the electronic structure which leads to a modification of the charge carriers effective mass. The last few years have seen a rising interest in the piezoresistive properties of semiconductor nanostructures, motivated in large part by claims of a giant piezoresistance effect in Silicon nanowires that is more than two orders of magnitude bigger than the known bulk effect. This review aims to present the controversy surrounding claims and counter-claims of giant piezoresistance in Silicon nanostructures by presenting a summary of the major works carried out over the last 10 years. The main conclusions that can be drawn from the literature are that i) reproducible evidence for a giant piezoresistance effect in un-gated Silicon nanowires is limited, ii) in gated nanowires a giant effect has been reproduced by several authors, iii) the giant effect is fundamentally different from either the bulk Silicon piezoresistance or that due to quantum confinement in accumulation layers and heterostructures, the evidence pointing to an electrostatic origin for the piezoresistance, iv) released nanowires tend to have slightly larger piezoresistance coefficients than un-released nanowires, and v) insufficient work has been performed on bottom-up grown nanowires to be able to rule out a fundamental difference in their properties when compared with top-down nanowires. On the basis of this, future possible research directions are suggested.
We study by means of density-functional calculations the role of lateral surface reconstructions in determining the electrical properties of <100> silicon nanowires. The different lateral reconstructions are explored by relaxing all the nanowires with crystalline bulk silicon structure and all possible ideal facets that correspond to an average diameter of 1.5 nm. We show that the reconstruction induces the formation of ubiquitous surface states that turn the wires into semi-metallic or metallic.
We report on the heterogeneous nucleation of catalyst-free InAs nanowires on Si (111) substrates by chemical beam epitaxy. We show that nanowire nucleation is enhanced by sputtering the silicon substrate with energetic particles. We argue that particle bombardment introduces lattice defects on the silicon surface that serve as preferential nucleation sites. The formation of these nucleation sites can be controlled by the sputtering parameters, allowing the control of nanowire density in a wide range. Nanowire nucleation is accompanied by unwanted parasitic islands, but by careful choice of annealing and growth temperature allows to strongly reduce the relative density of these islands and to realize samples with high nanowire yield.
The hysteresis curves of multilayer microwires consisting of a soft magnetic nucleus, intermediate non-magnetic layers, and an external hard magnetic layer are investigated. The magnetostatic interaction between magnetic layers is proved to give rise to an antiferromagnetic-like coupling resulting in a magnetostatic bias in the hysteresis curves of the soft nucleus. This magnetostatic biasing effect is investigated in terms of the microwire geometry. The experimental results are interpreted considering an analytical model taking into account the magnetostatic interaction between the magnetic layers.
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