Simulation And Fabrication Of C/Mg₂Si/Si Heterojunction Photodetector

Mg₂Siis an indirect bandgap environmentally friendly semiconductor material,which has been extensively studied in thermoelectric materials,battery materials,structural materials,composite materials and other aspects.C,Mg and Siare non–toxic,pollution–free,and rich in the earth’s crust,showing environment–friendly and sustainable development characteristics.Mg₂Sihas a band gap width of 0.6–0.8 e V,and a high absorption coefficient of over 10⁵cm^–1 near 500 nm.The detection wavelength range is 400–1500 nm,which can extend the photoresponse cutoff wavelength of existing silicon photodetectors（PDs）to more than 1100 nm.It has great potential to become a substitute for other toxic,harmful,and high–cost heterojunction PDs for visible and near infrared light detection.In this paper,the model of Mg₂Si/Si,Graphene/Mg₂Si/Si,and Multilayer Graphene（MLG）/Mg₂Si/Siheterojunction PDs are established,and the detection properties of the PDs are studied.The models of MLG/Mg₂Si/SiO₂ and MLG/Mg₂Si/Al₂O₃ heterojunction PDs are established and their detection properties are studied.A Mg₂Si/Siheterojunction PD is prepared by magnetron sputtering and annealing process,and a C/Mg₂Si/Siheterojunction PD is prepared by transferring few–layer of Graphene to the Mg₂Si/Siheterojunction substrate by Suspended Self–help Transfer Few–layer Graphene.The detection properties of Mg₂Si/Siand C/Mg₂Si/Siheterojunction PDs are tested and analyzed.The details are as follows:（1）The PN and PIN structures of Mg₂Si/Siheterojunction PDs are established,and their detection properties are calculated.The results show that compared with PN structure,the performance of reverse breakdown voltage,forward conduction voltage,responsivity,EQE,response time and recovery time of PIN structure are improved,but the performance of dark current,NEP,D*,and on/off ratio become worse.PN type is characterized by low dark current but slow response.The characteristic of PIN type is that the lower junction capacitance can obtain faster response,but the dark current will become larger.The appropriate simulated doping concentrations and thicknesses conditions for the wavelength distribution corresponding to the peak of the PD’s detection properties in the near–infrared region are as follows:Siand Mg₂Silayer doping concentrations are 10¹⁷ cm^–3,and 10¹⁶ cm^–3,respectively,and Mg₂Silayer thickness is 3μm.At this time,the peak responsivity is 0.69 A/W and the peak EQE is 87%.The peak wavelengths are near 1000 nm,which belong to the near infrared region.The suitable simulated doping concentrations and thicknesses conditions for the wavelength distribution corresponding to the peak value of the detection properties of the PD in the visible region are as follows:the doping concentrations of Siand Mg₂Silayer are 10¹⁶cm^–3 and 10¹⁷ cm^–3,respectively,and the thicknesses of Siand Mg₂Silayer are 300 nm and 280 nm,respectively.At this time,the peak responsivity is 0.46 A/W and the peak EQE is 93%.The peak wavelengths are around 600 nm,which belongs to the visible region.The thickness can affect the absorption position of peak wavelength.The doping concentrations can affect the distribution of the barrier region,thus affecting the separation of photogenerated carriers.The two traditional methods of thickness and doping concentrations can realize the modification and regulation of the detection properties of Mg₂Si/Siheterojunction PD.It provides theoretical basis for the preparation of Mg₂Si/Siheterojunction PD.（2）The models of Graphene/Mg₂Si/Siand MLG/Mg₂Si/Siheterojunction PDs are established,and their detection properties are studied.The results show that compared with Mg₂Si/Siheterojunction PD,the detection properties of Graphene/Mg₂Si/Siand MLG/Mg₂Si/Siheterojunction PDs are significantly enhanced.The peak responsivity and EQE of the MLG/Mg₂Si/Siheterojunction are 0.84 A/W and 107%,respectively.A high built–in electric field is formed at the MLG/Mg₂Siinterface,which is beneficial to the separation of photogenerated carriers,thus improving the photocurrent,responsivity and EQE of the PDs.The results show that the design method of introducing Graphene to control the detection properties of Mg₂Si/Siheterojunction PD is feasible.The models of MLG/Mg₂Si/SiO₂ and MLG/Mg₂Si/Al₂O₃ heterojunction PDs are established and their detection properties are studied.Compared with MLG/Mg₂Si/Siheterojunction PDs,the responsivity and EQE performance of MLG/Mg₂Si/SiO₂ and MLG/Mg₂Si/Al₂O₃ heterojunction PDs are poor.The high potential barrier and deep potential well are formed at the interfaces of Mg₂Si/SiO₂ and Mg₂Si/Al₂O₃,which are not conducive to the effective separation of photogenerated carriers.It shows that it is more suitable to select Sisubstrate to prepare PDs.The above results provide theoretical basis for the preparation of C/Mg₂Si/Siheterojunction PD.（3）After optimizing and improving the sputtering structure of heterojunction,a p–Mg₂Si/n–Siheterojunction PD is fabricated by magnetron sputtering method and annealing process.The spectral response ranges from 700 to 1500 nm.The peak responsivity,EQE,NEP,D*,on/off ratio,dark current,and photocurrent are 14.76m W/A,1.6%,1.36×10^–12 WHz^–1/2,0.74×10¹⁰ Jones,2341,1.26 n A,and 2.95μA,respectively.The peak responsivity and EQE of the improved PD are 79 times and 70times higher than those of the unimproved PD,respectively.After the n–Mg₂Si/n–Sistructure is transformed into the p–Mg₂Si/n–Sistructure,the energy band at the Mg₂Siinterface bends downward to form a potential barrier,which is beneficial to the effective separation and transfer of photogenerated carriers,and the detection properties are improved.The results show that the experimental fabrication of Mg₂Si/Siheterojunction PD is feasible.（4）Few–layer of Graphene is transferred to the Mg₂Si/Siheterojunction substrates by the method of Suspended Self–help Transfer Few–layer Graphene,and then the C/Mg₂Si/Siheterojunction PD is prepared.The spectral response ranges from700 to 1500 nm.The peak responsivity,EQE,NEP,D*,on/off ratio,dark current,and photocurrent are 23.7 m A/W,2.75%,8.13×10^–13 WHz^–1/2,0.12×10¹¹ Jones,4086,1.16n A,and 4.74μA,respectively.Compared with the Mg₂Si/SiPD,the responsivity,EQE,NEP,D*,on/off ratio,dark current,and photocurrent of the C/Mg₂Si/SiPD are improved by 60.56%,71.88%,40.22%,62.16%,74.54%,8%,and 60.67%,respectively.Graphene has a tunable Fermi level and a high built–in electric field at the C/Mg₂Siinterface,which helps efficient photocarriers to be separated.With the increase of the number of Graphene layers,the light absorption of the PD will be enhanced,which is conducive to the improvement of photocurrent,responsivity and EQE.The decrease of dark current is conducive to the improvement of NEP and D*.The results show that the preparation technology of introducing Graphene to regulate the detection properties of Mg₂Si/SiPD is feasible.