Electrical investigation of black phosphorus and other low-dimensional materials

Abstract

Currently, semiconductor technology has reached the limit of development with a silicon-based three-dimensional structure. Future devices require novel properties that are usually not compatible with silicon, such as flexibility, transparency, and fast mobility. Several studies are being conducted on low-dimensional materials to create devices that can overcome the limitations of silicon. Low-dimensional materials are not simply small-sized materials. If one or more of the dimensions are small enough, physical properties that were not observed in the bulk state begin to appear. For example, graphene has very high mobility, transparency, and flexibility, but bulk graphite does not have these properties. Because of these properties, graphene has been regarded as a candidate material for the future device. However, graphene has been found that it is a semimetal material with a zero band gap. Therefore, graphene possesses various drawbacks for its electronic applications. This thesis mainly presents the electrical investigation of black phosphorus (BP). BP, a layered material with phosphorus, is a more suitable material than graphene for semiconductor device applications because of its suitable bandgap and other related properties. Even though various studies on BP have shown its great potential in electronics, there is a critical issue on BP research and applications. Researchers have found that BP undergoes degradation with exposure to ambient condition. To overcome the degradation issue, most of other studies focused on the prevention of BP degradation using the method of encapsulation. In contrary, to understand the degradation process of BP in detail, we take a different study method. In particular, we study the degradation behaviors of BP on various surface-functionalized substrates. We find that the hydrophobicity of the substrate is one of the most important factors to determine the degradation speed and behaviors of BP. We attribute this observation to the different water molecule diffusion depending on the surface hydrophobicity. In addition, this thesis also contains experimental results on other materials such as germanium selenide (GeSe) and silver cyanide (AgCN). We experimentally demonstrate that GeSe is a material with high photo-responsivity. On the other hand, we find that AgCN is an electrically insulator. To study these various materials, we also develop a facile device fabrication process, which can minimize the exposure to the ambient conditions and chemical treatment.