Synthesis and characterization of Fe/Si-based functional nanostructures

In the field of microelectronics, new materials and device architectures are required to control and improve device performance. This work focuses on the preparation of Fe/Si nanostructures using bottom-up and top-down nanofabrication approaches.

A bottom-up nanofabrication approach involving self-assembly was used to prepare the ensembles of α-FeSi2 and β-FeSi2 iron silicide nano- and submicron crystallites on gold-activated and gold-free Si(001), Si(110), Si(111) surfaces at different Si/Fe flux ratios and different substrate temperatures. The study reveals that using gold-assisted growth regulates the morphology of the resulting crystallites and preferred orientation relationship (OR) of the α-FeSi2(001) lattice plane parallel to the Si substrate surface. The resistivity value of the
α-FeSi2/Si system increases as the angle between the conductivity channels in α-FeSi2 and the high-conductivity directions in Si increases. A prepared FeSi2/Si system can be considered as a system of back-to-back connected Schottky diodes and used when another Schottky contact with lower-barrier height in semiconductor devices may substitute the ohmic contact.

A top-down nanofabrication approach was used to prepare silicon nanowire (Si NW)-based
Indium-back-gate field-effect transistors (FET) with Schottky contacts on silicon-on-insulator (SOI) substrates with Fe source and drain contact pads and varied Si NW widths. Due to modifications in the technological procedure, an Fe/Si contact area was formed under the Fe film, which led to prepared devices demonstrating relatively low Schottky barrier heights of 0.05-0.1 eV. The devices exhibit ambipolar behavior independent of the gate polarity, and the current is influenced by the back-to-back Schottky diodes formed by the source (S) and
drain (D). Based on the source-drain current changes, the resulting devices are applied for biomolecular detection. The functionalization of the Si NW surface was performed using a dip-pen nanolithography process.

This thesis introduces the factors that significantly contribute to the electrical resistivity in the FeSi2/Si system and are important to consider for predicting the electrical properties of the system and designing contacts in microelectronic devices. The proposed version of Si NW FET with Fe S/D contacts is a promising prototype for the realization of detectors and sensors for biological compounds.


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