ULTRATHIN BLACK PHOSPHORUS: A NEW HIGH-MOBILITY TWO-DIMENSIONAL SEMICONDUCTOR

Abstract

Black phosphorus is the crystalline and most stable allotrope of the chemical element P at ambient conditions. The crystal is a known narrow-gap semiconductor. This thesis describes the isolation of two-dimensional sheets of black phosphorus with sub 10 nanometer thickness, and the study of the ultrathin material’s electrical properties in field-effect devices. The exfoliated crystal is found to degrade under ambient conditions. The crystal is passivated using dry transfer of graphene or hBN in inert atmosphere, which allows studying the properties of the pristine material. The degradation process is found to affect the electronic properties by causing unintentional p-doping and suppressing the n-type transport. Finally, a method is developed to controllably dope ultrathin black phosphorus using deposition of Cu ad-atoms. The experiments and critical discussions aim to analyze the application prospects of ultrathin black phosphorus as a novel two-dimensional semiconductor material.