Plasmon induced optoelectronic devices based on two-dimensional materials

Abstract

As the rea of the 4th industrial revolution opens, optical convergence technology aims to increase the performance of existing products or create new produces by combining a various technologies. As technology development progresses, the fundamental products such as laser, LED, and photodetector should also be upgraded. The photodetectors plays an important role in converting the optical signal into an electrical signal in the field of optoelectronics including optical communication. High performance photodetector is essential for realizing the future optical technologies because photodetectors should be able to detect the rapidly changing light signals. Silicon-based photodetector has widely used because of the easy fabrication, low cost and integrity with other electrical devices. However, silicon has intrinsically low photo-responsivity and detecting range is limited by the presence of bandgap. For this reason, graphene has attracted attention in the fields of photodetectors because of their unique properties of electrical, optical and mechanical. Despite these excellent properties, short carrier lifetime and low light absorption rate have limited application as an optical devices. Following a significant number of graphene studies, other two-dimensional semiconductors have opened a window for realizing novel optoelectronic devices. Similar to graphene, being atomically thin, these materials exhibit a wide range of unique properties which cannot be seen in three-dimensional bulk materials. These two-dimensional materials can overcome the drawbacks of short carrier lifetime of graphene, but still have limited by the low light absorption due to the atomically thin nature. In this thesis, we use plasmons as a way to overcome the limitation of absorption rate. Plasmon can trap light on the surface of metallic materials, which can increase the absorption rate in the vicinity of metal. One effective ways to enhance the plasmonic field is to place two metal nanoparticles close together by trapping the light inside the spacer of separation. However, it is very difficult to place two nanoparticles close each other in nanoscale fabrication. So, we use two-dimensional material as a spacer to separate two closely packed nanoparticles. In general, the intensity of plasmon resonance increases as the distance between two nanoparticles decreases, so the two-dimensional material having an atomically thin thickness can be a good candidate for enhancing plasmonic resonance. This paper start with the method that enhancing the gap-mode plasmon and the plasmon tunneling phenomena which occurs in very thin thickness of spacer. Based on these prior studies, gap-mode plasmons are applied to photodetectors. By introducing the gap-mode plasmon, the performance of the photodetectors is significantly increased, and the proposed device structure has shown the possibility of overcoming the trade-off relationship between photoresponsvity and response time. Finally, the non-ideal phenomenon of the photodetector caused by photocarrier trapping in two-dimensional materials is analyzed.