Titanium silicide islands on atomically clean Si(100): Identifying single electron tunneling effects

Abstract

Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (< 2 nm) on atomically clean Si(100) substrates followed by annealing to ~800ºC. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET.Some of the islands formed are small enough (diameter < 10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did not do so, and the reasons for the absence of observable SET are evaluated. The most likely reasons for the absence of SET are determined to be a wide depletion region in the substrate and Schottky barrier lowering due to Fermi level pinning by surface states of the clean silicon near the islands.The results establish that although the Schottky barrier can act as an effective tunnel junction in a DBTJ structure, the islands may be unreliable in future nanoelectronic devices. Therefore, methods are discussed to improve the reliability of future devices.

RuO2/TiSi2/graphene composite for enhanced photocatalytic hydrogen generation under visible light irradiation

“…20,31 In addition, functionalized graphene by organic sensitizer molecules can promote photocatalytic activity for hydrogen evolution due to harvesting the light irradiation of the sensitizers. 32,33 Titanium disilicide (TiSi 2 ) is an excellent semiconductor material due to its thermodynamic stability, single electron tunneling characteristics, 34 and unusual optoelectronic properties. TiSi 2 with the bandgap from 1.5 to 3.4 eV, absorbs visible and near-UV range of the solar spectrum.…”

WS2 as an Effective Noble-Metal Free Cocatalyst Modified TiSi2 for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

“…Titanium disilicide (TiSi 2 ) is an excellent semiconductor material due to its high thermodynamic stability and excellent optical properties [13]. The band gap of TiSi 2 is in the range of 1.5 to 3.4 eV, suggesting that the absorption spectrum of TiSi 2 can cover almost the whole visible range and a part of the ultraviolet.…”

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)

“…Hence, it is surprising to observe a strong electronic coupling between the CoSi 2 islands and the silicon substrate in our experiment for both biases. Moreover, when a strong electronic decoupling is observed on other silicide islands types, , it is explained that the lack of conductance arises from the increasing bulk band gap energy of the silicon sample, in particular, when the temperature decreases . Yet, this effect is only treated in terms of interface state at the silicide–silicon interface boundary.…”

“…Moreover, when a strong electronic decoupling is observed on other silicide islands types, 25,51 it is explained that the lack of conductance arises from the increasing bulk band gap energy of the silicon sample, in particular, when the temperature decreases. 52 Yet, this effect is only treated in terms of interface state at the silicide−silicon interface boundary. Consequently, the understanding of the electronic transport that occurs from the silicide−silicon interface to the metallic contact that holds the entire sample at a macroscopic scale is a puzzling problem, in particular, at the silicon gap energy range.…”

“…The Schottky barrier energy is usually relatively high (i.e., can reach several hundreds of millivolts), which often limit a general use of these structures for nanoscale ohmic contacts at room temperature. − On another side, it has been shown that the electronic properties of various silicide islands, such as TiSi 2 , can be electronically decoupled from the supporting semiconductor. This effect occurs because of the rising band gap energy of the substrate at low temperature, pointing out the lack of electronic conducting channels within this energy range. , Hence, the creation of electronic conducting channels that warrant a good electronic transport from the silicide–silicon interface into the silicon sample is difficult to control. In this work we have shown that the growth of individual nanometer-scale CoSi 2 silicide islands is performed via reactive deposition epitaxy methods.…”