渦旋光增強奈米矽線與二硫化鉬場效電晶體之光導電度

Abstract

光可以帶有自旋與軌道角動量，分別體現於圓偏振以及渦旋光上。軌道角動量的光在理論上擁有無限的自由度，預期可以應用於光通訊的領域。此外，光額外的軌道角動量會引發電子躍遷形式的改變，進而影響電子激發至導帶的濃度，改變光電流的大小。在這篇論文中，Silicon Nanowires以及MoS2所製成的場效應電晶體被用來感測光的軌道角動量。電性上的結果顯現，光電流隨著軌道角動量的變大而上升；該現象，可以被歸因於軌道角動量的光增強了材料對光的吸收率，使得光電流來源於光導效應(Photoconductive Effect)和光閘效應(Photogating Effect)的現象被提高。不同軌道角動量的光所引發之光電流隨著光強的變化，亦證明了該現象。透過這份研究，可以預期除了光強與頻率，未來可以把光的軌道角動量當作一個額外的自由度來去調控材料的光電流。

Light can possess spin and orbital angular momentum (OAM), which can be manifested in circularly polarized light and twisted light (TL), respectively. TL is expected to be applicable in the field of Opto-Communication owing to its theoretically infinite degree of freedom. The extra angular momentum of light will induce different transition paths, impacting the concentration of electrons in the conduction band, which leads to a potential application in modulating the electrical current. In this thesis, phototransistors made from Silicon Nanowires and MoS2 are used to detect the OAM of light. We have observed a progressively increasing photocurrent when incremented the light’s OAM; such phenomenon is attributed to the photoconductive and photogating effects due to enhancing absorption of TL. In photocurrent’ power dependence as a function of OAM light, we have noticed the linear power dependence in plane wave light, but sublinear behavior when using TL, indicating the density of holes in trap states is increased. Through this research, a further application can be developed by utilizing the OAM of light as a degree of freedom to control the signal from photodetectors.