Two-dimensional Material/silicon Heterojunction Photodetector Research

Photodetectors are closely related with our daily life and applied in various fields,such as optical imaging,communications,biomedicine,etc.Two-dimensional?2D?materials show excellent optoelectronic properties arising from quantum confinement effect.This way,they become the potential candidate materials for next generation optoelectronics.Due to the easy fabrication of 2D materials based heterostructure originating from the weak van der Waals interaction between layers,it has attracted much attentions.Graphene?Gr?,a kind of 2D material,shows high carrier mobility,wide response spectrum.However,the light absorption of a single layer is only 2.3%.As a result,photodetectors made from graphene always have low responsivity.Transitional metal dichalcognides?TMDCs?show strong light-matter interaction and the light absorption at resonant exciton frequency can exceeds 10%for a single layer.However,TMDCs have a relatively low carrier mobility.Utilizing the easy integration of 2D materials with Si,and the pros of graphene and TMDCs,high performance photodectors is anticipated from the heterostructure.Based on the above considerations,the main contents of this paper are as follows:?1?Fabrication of Gr/Si Schottky junction photodetectors.The device shows broadband detection covering visible to near infrared light.The maximum responsivity of the device is 0.24 A/W?area 3.14 mm²,800 nm,0.2 V?.The device shows obvious photovoltaic effect and has obvious response to weak light?57 nW?.?2?Synthesis of WS₂ single crystal by CVD.The largest single layer triangle on the silicon oxide substrate is about 220?m.Double-layer WS₂,WS₂ crystal particles,a combination of 1D nanowires and 2D nanosheets can be obtained by tuning the growth condition.Furthermore,it is found that high quality transfer of WS₂ can be achieved by using PMMA/PS double layer protecting polymer film.?3?Enhancing the photodetection performance of Gr/Si heterostructure by inserting a layer of WS₂.The maximum responsivity of the device is 54.5 A/W?800 nm,0.3 V?,which is 2 orders of Gr/Si heterojunction device and commercial silicon diode photodetectors.?4?Photocurrent generation position of the device is tested using photocurrent mapping technology.It is confirmed that the photocurrent of the Gr/Si heterojunction in the silicon oxide region is stronger than that in the silicon region.As the bias voltage increases,the Gr/WS₂/Si heterojunction has the same order of photocurrent generation at the silicon oxide position.Combined with the reported results from literature,the presence of photocurrent in Gr/WS₂/SiO₂ area is caused by electrostatic field effect combined with the diffusion of carriers underneath the SiO₂.