Light-Lattice Interactions in Atomically Thin van der Waals Semiconductors toward the Controlled Doping Characteristics

Abstract

Since the report on graphene in 2004, interest in two dimensional materials has increased and active research has been conducted. The two-dimensional materials have been continuously highlighted as new electronics and optoelectronics because of their novel properties stemming from their unique structure. Among them, semiconductor trigonal prismatic phase transition-metal dichalcogenides, MX2 (M= Mo, W; X= S, Se, Te), have attracted attention especially as new device materials having a finite band gap in the visible and near-infrared light range. Along with the increasing interest in two dimensional semiconductor transition-metal dichalcogenides, studies on the large-area vapor phase synthesis of the materials and the possibility of their device applications have been actively conducted. On the other hand, until now, few studies on implementing a monolithic integrated circuits using the large area synthesized two dimensional semiconductors have not been reported yet. This dissertation concerns introducing a new concept of circuit writing on two dimensional semiconductor transition-metal dichalcogenides by light illumination and defect inducing. For that, first of all, the previous strategies for doping in two dimensional semiconductor materials and the doping characterization methods will be summarized. Then, another new doping methodology, called light-induced local doping, will be introduced in the following chapters. According to our light-induced doping method, semiconductor phase molybdenum ditelluride (MoTe2) and tungsten diselenide (WSe2) can be effectively doped by light illumination. More interestingly, the polarity of doping, p-type or n-type, can be defined selectively by the wavelength, or the color of the light. Our experimental results show that visible light (532 nm) illumination convert the channel to p-type, and ultraviolet (355 nm) illumination converts it to n-type. Then, the atomic scale origin of the light induced doping has analyzed using scanning tunneling microscopy and transmission electron microscopy. Following the results of atomic scale analysis, photochemical bond dissociation incorporated point defects are the origin of n-type doping, whereas oxygen incorporated point defects are the origin of p-type doping. Using this light-color dependent local doping method, we could successfully demonstrate the writing of monolithic integrated circuits on two dimensional semiconductor materials. As an examples, we introduce the results of writing integrated circuit components, such as p-n diode, bipolar junction transistor, and CMOS inverter.