Silicon nano-wires (SiNWs) have attracted the attention of many researchers due to their structural, optical, electrical and thermoelectric properties. They are expected to be important building blocks in the future nano-electronic and photonic devices including solar cells, field-effect transistors, memory devices and chemical and biomedical sensors. Owing to their compatibility with the Si-base technology, SiNWs can be used not only as the functional units of the devices but also as the interconnects [1–6].
Various methods have been reported for SiNW fabrication, including both bottom-up and top-down techniques. Bottom-up growth methods include laser ablation, evaporation, solution-based methods and chemical vapour deposition (CVD). The CVD growth usually takes place via vapour-liquid-solid (VLS) route . Many catalyst materials, mainly metals including Au, Al, Ni, Fe and Ag, have been used for the SiNW growth [1, 8]. Among these metals, Au as catalyst has been the most popular and most widely investigated due to its chemical inertness and low eutectic temperature of Au-Si system. However, Au introduces deep impurity levels in Si bandgap and degrades the charge carrier mobility . Therefore, alternative catalyst investigation is of crucial importance.
One of the important parameters when considering the nano-wire fabrication process is the growth temperature, as this can determine the variety of substrates that could be used, especially when there is a prefabricated layer of some temperature-dependent material. The nano-wire growth temperature is determined by the eutectic temperature of the catalyst-precursor alloy ; thus, the low-temperature growth will depend on the appropriate catalysts choice. Considering the characteristics of Ga, including the Ga/Si alloy low eutectic point of 29.774°C, wide temperature range for silicon solubility and its non-reactivity to form solid compound with silicon, Ga has been suggested as a good alternative to Au to grow SiNWs at low-temperatures. It is important to note that Ga does not act as catalyst for the decomposition of precursor gas as it does not assist the dissociation of SiH4 below its thermal decomposition point. Therefore, Ga acts only as a solvent, and the decomposition is achieved by plasma treatment (by the use of plasma-enhanced chemical vapour deposition (PECVD) system) .
In this study, Ga catalyst is used with an aim to grow SiNWs at a lowest temperature using PECVD technique. The growth temperature was varied between 100°C and 400°C. The grown nano-structures were characterised using scanning electron microscopy (SEM), Ultra Violet Visible spectroscopy (UV-Vis) and Raman spectroscopy.
Electronic memory devices play a vital role in our everyday life. In the last a few decades, major progress has been observed focusing on the miniaturisation of the memory size cell while increasing its density. However, materials and fabrication techniques are reaching their limits. Alternative materials and architecture of memories, as well as manufacturing processes, are considered. In order to achieve this, different types of memories such as polymer, phase change and resistance have been reported in the literature [11–13]. Two-terminal non-volatile is one of the most promising memory types for fulfilling the aim of combining low cost, high density and small size devices . Therefore in this study, we present a two-terminal non-volatile memory based on SiNWs. The suitability and potential use of SiNWs for storage medium are investigated. The electrical behaviour of these devices was examined mainly in terms of current–voltage (I V) characteristics and data retention time (current-time) measurements.
Schottky diodes made of bulk materials do not dissipate heat quickly; hence, performance and lifespan of the device are reduced. Recently, one-dimensional (1D) nano-structures and their incorporation into Schottky diodes have been studied extensively. Due to their high surface-to-volume ratio and space between the nano-wires, diodes made of 1D nano-structure arrays can dissipate heat faster due to individual input from each wire. Therefore, integration of these nano-materials into the device will enhance its performance and lifespan . The as-grown SiNWs fabricated in this study were also used in a Schottky diode, and the electrical behaviour of the device is analysed.
Solar cells fabricated with nano-wires have shown several advantages when compared to wafer-based solar cells; some of them include trapping of light, less reflection and enhanced bandgap tuning. Although these advantages do not compete to attain efficiency more than efficiencies reported until today, they help in obtaining same efficiency or less by reducing the quantity and quality of the material. Nano-wires deposited by our growth method can have a number of benefits due to their possible fabrication directly on cheaper substrates including steel, bricks, aluminium foil and conductive glass, thus reducing the price of the solar cells based on these structures. In this study, SiNW-based Schottky solar cells were fabricated and their performance tested.