Study On Gr/Si Schottky Junct Lotodetector

In this paper,Graphene(Gr)/Si Schottky junction photodetector is studied.Devices are fabricated and tested.From the band energy perspective,I-V,C-V characteristics of the device,effects of Gr/SiNx/Si(Metal-Insulation-Semiconductor)capacitor on the device and the improvement of Al2O3 interface layer on the device are investigated.Firstly,experiment methods are introduced,including device technology involved in the process of device fabrication,transfer of Gr,characterization of Gr and Schottky junction that of the basic principle of Gr/Si photodetector.Then,I-V and C-V characteristics of Gr/Si photodetector are analyzed.Under the illumination of 808 nm near-infrared light,the photodetector exhibits that the reverse photocurrent is approximately the same value as the forward one owing to photo-generated holes,which diffuse from Si/SiNx interface to Gr/Si junction and the responsivity is 0.26 A/W.The Schottky barrier height and ideality factor extracted from I-V dark current curve are 0.859 eV and 2.3 respectively based on thermionic emission model.The Schottky barrier height extracted from C-2-V curves on account of the equation of depletion layer capacitance increases and tends to be stable around 0.82 eV with increasing frequency.The value of depletion layer width of Gr/Si Schottky junction increases with increasing frequency,while doping concentration of Si donor atoms and capacitance of device decrease,which are attributed to surface statesFinally,from the perspective of interface engineering,photodetector is improved by introducing the Al2O3 layer with controllable thickness between Gr and Si using atomic layer deposition technology.The results show that compared with Gr/Si photodetector without Al2O3,the dark current of that with 3 nm Al2O3 decreases more than one order of magnitude,Schottky barrier height increases from 0.859 eV to 0.910 eV.Higher Schottky barrier height facilitates the separation of electrons and holes and reduces interface recombination.It is obvious that light responsivity increases from 0.26 A/W to 0.44 A/W.Due to the influence of interface defects,the capacitance appears a peak value,and the ideal factor increases from 2.3 to 5.38.When the thickness of Al2O3 layer decreases from 3 nn to 2 nm,the dark current increases,while the light responsivity increases from 0.44 A/W to 0.62 A/W.Because thicker interface layer hinders the tunneling of the holes,leading to the hole accumulation at Al2O3/Si interface.Then electrons and holes recombine intensely,photocurrent reduces.