Synthesis and electrical characterization of one-dimensional van der Waals semiconductors
Over the past decades, electronic devices have scaled to a few tens of nanometers to increase processing power and reduce energy consumption. However, conventional silicon devices reached the quantum limit, and we need to find alternative materials or quantum devices. One possible solution is to use van der Waals (vdW) nanomaterials, particularly one-dimensional (1D) nanowires. Unlike the traditional silicon nanowires having surface dangling bonds (chemically active), vdW nanowires maintain their intrinsic properties because of their inert surface originating from the vdW bonds (chemically inactive). However, there are some challenges in creating devices using vdW nanowires. This dissertation aims to tackle two of them: (1) Achieving large-scale synthesis of vdW nanowires, (2) Understanding the electrical properties of the interface between nanowires and metal. For large-scale integration, we need high-quality nanowires of macroscopic length. There are several prospective synthesis methods inspired from traditional nanowire growth. So far, there is no experimental realization of synthesizing ultralong vdW nanowires. This study focusses on developing new synthesis methods to achieve that. Using a simple solid-state reaction growth, Ta2Ni3Se8 (TNS) nanowires with lengths of several millimeters were obtained. Further, we demonstrated that TNS could be mechanically exfoliated into thinner nanowires with a thickness down to a few nanometers. To realize TNS nanowire based electronic devices, we need to understand the interface at the TNS/Metal. There is a broad range of metals to study the electrical functionalities and chemical nature of the interface. To achieve strong bonding, Nickel is chosen as the contact metal. By analyzing the I-V characteristics of nanodevices, electrical contact between Ni and TNS is found to be Schottky type with a barrier height of 0.4 eV. The device is persistent and stable, evidenced from I-V characteristics and extracted Schottky barrier. These findings will advance the application of TNS nanowires in photodetectors, solar cells, and chemical sensors. Next, we studied TNS devices with Copper (Cu) contact. It is revealed that TNS/Cu interface form low-resistance Ohmic contact. Through the variable length resistance method, the contact resistance is found to be as low as 500 Ω, which contributes to less than 2% of the total resistance of the device. Also, low-temperature measurements revealed that copper maintains ohmic contact down to ~20K. These findings pave the way for further investigations of intrinsic properties and the development of TNS logic devices.