Research And Design Of High-performance Photodetector

Photodetectors are key components in optical communications,and they play a pivotal role in fields such as communications,military,medical monitoring,and space exploration.With the development of communication speed and communication quality,the responsivity and specific detection rate of photodetectors need to be improved.Transition metal sulfide ultra-thin two-dimensional materials such as MoS₂,has great application potential in the field of photoelectric detection.The way to break the theoretical limit of the sub-threshold swing of the traditional avalanche photodetector(60m V/dec),achieve an external quantum efficiency of over 90%and a specific detection rate of 10¹²while the optical gain reaches the order of 10⁵,is an important issue to be solved at present.In this thesis,the equivalent model of the photodetector has been established.The simulation tool COMSOL has been used for multi-physics coupling and simulation.Through the comparison of two-dimensional materials,suitable materials are selected to construct heterojunctions,surface plasmon resonance is introduced,and methods that may be used to reduce the subthreshold swing of devices are studied.The addition of graphene provides new ideas for solving the problems of two-dimensional material avalanche photodetectors with an external quantum efficiency of less than90%and a light responsivity of less than 10A/W.First,ultra-thin MoS₂has been taken as the object,BP with high mobility in the vertical direction is selected,a BP/MoS₂van der Waals heterojunction model is constructed for multi-physics coupling simulation,and methods to improve the photoresponse of photodetectors are studied.The formation of a heterojunction with BP can effectively reduce the Johnson noise caused by the high dark current in the single-layer MoS₂photodetector.It has good sensitivity in the near-infrared band.BP/MoS₂van der Waals heterojunction can take into account the excellent performance of single-layer and multi-layer MoS₂.The theoretical limit of the sub-threshold swing of traditional avalanche photodetectors is60m V/dec.Some new tunneling devices can obtain sub-threshold swings lower than this theoretical value,but it is difficult to achieve fast time response,high light responsivity and high light gain at the same time.The band structures of BP and In Se are well matched,and the ballistic avalanche photodetector based on the BP/In Se heterojunction exhibits extremely high photon amplification.The noise is lower than the theoretical limit of the traditional avalanche detector,and the subthreshold swing is only 0.25m V/dec.Aiming at the problem that the BP/In Se heterojunction has extremely high optical gain but low optical responsivity,graphene is used on the basis of the original structure to construct a Gr/BP-In Se structure avalanche photodetector to simulate its electrical and optical characteristics.Compared with the BP/In Se heterojunction,the participation of graphene has greatly improved the infrared detection band of the Gr/BP-In Se structure avalanche photodetector.An Au-Gr-SiO₂tapered multilayer slit structure has been constructed,combined with the full absorption characteristics of graphene in the infrared band,extraordinary optical transmission was achieved.The finite element method is used to study the transmission spectrum and the normalized electric field distribution.By changing the width and height of the slit,the optimal structure model parameters are given,and the light absorption rate is improved.Compared with bare silicon film,by changing the radius and distance of the introduced Au nanoparticles,the light absorption rate and photoelectric conversion rate can be improved at the same time.This method based on surface plasmon resonance is expected to further improvement of the response performance of photodetectors.