High-sensitivity And Broadband Graphene Photodetector Enhanced By Pyroelectric Effect Of Lithium Niobate

Graphene shows excellent characteristics such as high carrier mobility,high transparency,wide spectral range of light absorption and zero band gap.The Fermi energy level of graphene can be adjusted,which has great application potential in the field of photodetector.However,the responsivity of traditional monolayer graphene photodetector is limited by the low absorption and the short interaction length with light.To improve the responsivity of graphene photodetector,fabricating a graphene heterojunction is one of the most effective ways.Ferroelectric materials such as lithium niobate can achieve high-performance heterojunction by doping graphene to obtain excellent optoelectronic devices.LiNbO₃ is a kind of ferroelectric and semiconductor material that has been widely studied in recent years due to its excellent ferroelectric,thermoelectric,electro-optical and piezoelectric properties.LiNbO₃ also shows unique property of spontaneous polarization,which can change the distribution and intensity of surface electrostatic charges.In this paper,x-cut LiNbO₃ is used to fabricate a high sensitivity and broadband photodetector by combing graphene.The pyroelectric polarization characteristic of LiNbO₃ is used to achieve the doping of graphene,which make it possible to obtain the heterojunction structure.The photodetector shows high sensitivity and broadband photodetection from visible light to near infrared?405-1064 nm?.In addition,the photodetector based on x-cut LiNbO₃ and graphene can operate without the external electric field.More specifically,the responsivity of the device is up to 10⁶ A/W,the external quantum efficiency reaches 10⁸%,and the detectivity reaches 10¹⁵Jones.The response time is evaluated to be millisecond.The results of the pyroelectric test of x-cut LiNbO₃ prove that the positive charge and negative charge are released in the direction of spontaneous polarization?z axis?when the device is illuminated,which can dope graphene.Graphene's zero band gap is susceptible to the doping charge because of the energy band structure.The Fermi surface moves down to form p-type doped graphene after doping with positive charges,and the Fermi surface moves up to form n-type doped graphene after doping with negative charges.Therefore,p-type doped and n-type doped graphene are formed along the spontaneous polarization direction of LiNbO₃.The change of electrical transport characteristics leads to the change in resistivity.Finally,the fabricated device produces a higher photoelectric response.The innovation in this paper is summarized as follows:1.The device is prepared by combining graphene with x-cut LiNbO₃,which can realize the P-type and N-type doping of graphene at the same time.2.The graphene based LiNbO₃ photodetector has a high response of 10⁶ A/W in the 405-1064 nm band with the ms level response time,which has realized the wide spectrum and high sensitivity detection.