Design Tunneling Transistor and Schottky Junction Solar Cell Using Van Der Waals Semiconductor Heterostructure

Abstract

Transition metal di-chalcogenide (TMDC) materials, being semiconductor in nature, offer Two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS2) possess unique and unusual properties that are particularly applicable to nanoelectronics and photovoltaic devices. In this dissertation, four different projects have been done that encompass the implementation of these materials to improve the performance of future transistors and Schottky junction solar cells. In chapter 2, an analytical current transport model of a dual gate tunnel field-effect transistor (TFET) is developed by utilizing the principle of band-to-band tunneling (BTBT) and MoS2 as the channel material. Later, using this compact model, both n-type and p-type TFETs are simulated to design the inverter, half adder circuit, and ring oscillator. From the simulation, it is concluded that the TFET is capable of switching with a very low subthreshold slope and demonstrates a high current on/off ratio, which eventually decreases the power consumption of the ring oscillator by one order of magnitude in comparison to the contemporary FET technologies. In chapter 4, an analytical model is developed to assess the photovoltaic performance of the concept: graphene/III-V semiconductor-based Schottky junction solar cells. Moreover, a heterostructure is proposed for possible solar cell application by adding the passivation and carrier selective layer to graphene/GaAs-based solar cells. The structure is simulated using both the analytical model and numerical tool (SCAPS) which show that a theoretical power conversion efficiency (PCE) of >18% is possible to achieve through this structural modification. TMDC materials with a particular thickness on the noble metal substrate have an exceptional ability to perform near-unity absorption at the visible wavelength spectrum. In chapter 5, a simulation is performed to find out the required thickness for which maximum absorbance of six TMDC materials on a gold substrate can be achieved. Later, using numerical software (SCAPS 1D), the J-V characteristics are simulated to find out the best possible combination (TMDC/metal) in terms of efficiency so that further improvement can be done in the future. In chapter 6, a facile method has been developed to do the direct deposition of graphene on a dielectric (SiO2) substrate using a cold-wall CVD system (Nano CVD 8G graphene reactor).