Evidence of Low Schottky Barrier Effects and the Role of Gap States in the Electronic Transport through Individual CoSi₂ Silicide Nanoislands at Low Temperature (9 K)

Abstract

In this paper, we study the electronic properties of CoSi 2 metallic islands grown on a Si(100) surface with a low-temperature (9 K) scanning tunneling microscope (STM). The atomic scale structures of the flat and ridge silicide islands surfaces are described with an ultimate resolution, thanks to the stability of low-temperature STM. A statistical study of the I−V and dI/dV signals acquired along the islands shows their metallic-like properties and a very small residual conduction band gap of ∼30 mV. This reveals that the electronic transport through the individual metallic islands at the silicide−silicon interface is mainly ruled by electronic tunnel processes for positive sample biases and driven by the presence of gap states for negative sample voltage. The role of the gap states is demonstrated by performing conductance measurements along the dimer vacancy lines in which interstitial Co atoms are accessible at the silicon surface. Hence, the electronic transport that occurs from the silicide−silicon interface toward the macroscopic contact of the sample can be explained.

Stability of Schottky and Ohmic Au Nanocatalysts to ZnO Nanowires

“…This increase in reverse-bias current is indicative of quantum-mechanical tunneling current-induced breakdown at the interface and as our previous work has shown tunneling is concentrated at the interface edge. , When the voltage sweeps approached 5 V there is a dramatic increase in reverse bias current typical of reverse-bias breakdown of Schottky contacts; however, on closer examination of the ±5 V curve, hysteresis is also evident in reverse-bias indicating some permanent change of the interface has occurred where the current reaches a maximum of −20 μA (this wire shows increased current carrying capability compared to the Ohmic nanowires that is potentially a result of the heating effect occurring at the Au–ZnO interface that is in thermal contact with the measurement probe rather than at the midspan of the nanowires with Ohmic contacts). Hysteresis in I – V characteristics is evidence of the trapping and releasing of charge carriers due to defects and is associated with tunneling through defect states . The permanent change is confirmed by comparing (Figure b) the ±3 (blue) before and ±1 V (red dashes-dots) curves that show the contact has lost much of its rectifying quality and in reverse-bias the ±1 V I – V behavior now traces that of the ±5 V curve.…”

“…Hysteresis in I−V characteristics is evidence of the trapping and releasing of charge carriers due to defects and is associated with tunneling through defect states. 54 The permanent change is confirmed by comparing (Figure 4b) the ±3 (blue) before and ±1 V (red dashes-dots) curves that show the contact has lost much of its rectifying quality and in reverse-bias the ±1 V I−V behavior now traces that of the ±5 V curve. However, it is notable that there is no change in the forward-bias I−V behavior for any of the I−V sweeps in this initial stage of experiments and the nanowire retains the same forward-bias behavior when current transport is dominated by thermionic-emission over the potential barrier spreading the current across the entire interface area, rather than tunneling through the barrier in reverse-bias at the perimeter of the nanowire-nanocontact interface.…”

Modifying the Interface Edge to Control the Electrical Transport Properties of Nanocontacts to Nanowires

“…Recent work on Au nanocontacts to ZnO nanowires has shown that the transport properties can be switched from ohmic to Schottky as a result of quantum-mechanical edge-tunneling effects by selecting a nanocontact that is comparable in diameter to the nanowire . In structurally controlled nanocontacts to planar surfaces, a change in electrical transport properties has been reported by varying the atomic structure of the interface. − Currently, efforts to control the transport properties of nanowire catalyst contacts are limited to changes in the interface dipole, achieved by metal alloying or heterostructure formation, and size effects that modulate carrier transport. ,, However, a number of techniques exist that could be exploited to control the electrical characteristics of the Au contacts such as etching, nanowire surface architecture modulation during growth, or the addition of nanowire shell materials. − Furthermore, there has been little detailed study of the transport behavior of nanowires with Au contacts in relation to changes in the atomic-scale structure and chemistry of the interface region. In this work, we investigate nanoscale modifications to the material at the interface edge of the Au–ZnO nanowire interfaces and directly relate the transport properties to the structure and form of the interface using aberration-corrected scanning transmission electron microscopy (ac-STEM).…”

“…This is apparent from the increased reverse-bias current relative to forward-bias current. In contrast, forward-bias transport is dominated by thermionic emission over the potential barrier that is limited after etching by the reduced interface size, reduced nanowire conductivity, and by an increased concentration of traps near the interface that are intrinsic and created by the degraded nature of the Au–nanowire junction. , These ideas are summarized in the band diagram (Figure e). The presence of defects are also evident from the hysteresis in the I – V characteristics of NW3 that signifies the trapping and release of charge carriers in addition to the comparably greater conductivity in reverse-bias when tunneling has a greater effect due to the thinner depletion region and downward shift of the semiconductor Fermi level.…”

A two-dimensional ON/OFF switching device based on anisotropic interactions of atomic quantum dots on Si(100):H

“…Hence, the unoccupied DOS peaks observed in the (d I /d V )/( I / V ) curves in Fig. 1 mostly arise from tunneling processes involving transport channels opening when the unoccupied Si-DB states energy match the ones of the As atoms, as it can be observed with gap states 36 . This effect is further demonstrated by the fact that no energy shift of the unoccupied Si-DB states is observed in the (d I /d V )/( I / V ) curves at the coupling areas when the STM tip height decreases (Supplementary Fig.…”