Research On Terahertz Photodetector Based On Graphene

The terahertz wave is widely used in imaging system,broadband communications and environmental monitoring fields due to its unique location in electromagnetic spectrum.Thus,the study of terahertz detection is gaining increasing attention around the world.Traditional terahertz detectors are commonly based on thermal sensing elements being either very slow or requiring deep cryogenic cooling due to limited detection performance.Graphene,an emerging two-dimensional?2D?material,has demonstrated its potential to be a promising candidate for terahertz detection due to its excellent properties.Graphene has extraordinary mechanical flexibility,fantastic thermal conductivity and ultrahigh carrier mobility.However,due to the responsivity of photocurrent or photovoltage is very limited for the low optical absorption of graphene,the responsivity of terahertz detectors still has a lot of room to be improved.Hence,device utlizing novel physical mechanisms are needed to improve performance of terahertz detectors for achieving any practical applications.The main work of this article is as follows:?1?A high efficient graphene/Al₂O₃/Ga As tunneling heterostructure has been realized as a terahertz?THz?wave detector at room temperature.The heterojunction formed by combining graphene with Al₂O₃ shows well rectification characteristics.The introduction of Al₂O₃ layer between graphene and bulk semiconductor can effectively decrease the dark current but does not reduce the photocurrent,thereby improve the performance of photoelectronic devices.The responsivity of our terahertz detector was measured 579.7 A/W at 0.29 THz under the forward bias voltage of 1.9 V,and the?2?Through the energy band diagram of the graphene/Al₂O₃/Ga As heterostructure to analyze the relationship between the device current and the applied bias voltage.Then,compare the theoretical analysis with experimental results.The process of tunneling effect is analyzed by energy band diagrams under zero bias?thermal equilibrium?,forward bias and reverse bias voltage.Theoretical analysis shows that the device has the most significant electron tunneling effect when the applied forward bias is 1.49 V,and the corresponding tunneling current is the largest.During the experimental test,it was found that the tunneling current was the biggeest at the applied bias of 1.9 V.It is because the contact resistance and the resistance of the N-type Ga As lead to a partial voltage,which causes the actual applied bias voltage to be slightly larger than the ideal bias voltage.?3?A quantum dot/graphene/oxide layer/semiconductor terahertz detector structure is proposed,and the effects of quantum dot concentration and oxide layer thickness on the terahertz detection effect are studied.Graphene quantum dots absorb terahertz wave photon energy to generate photo-generated carriers.The carriers are separated at the interface between the quantum dots and graphene,and the holes flow to graphene.From the analysis of the I-V characteristic curve,we know that the higher the concentration of quantum dots,the more obvious the detection effect of the detector;the detection effect of alumina at 10 nm is better than that at 20 nm.