Preparation And Device Properties Of MoSe₂/WSe₂ P-n Heterojunctions

Two-dimensional transition metal chalcogenides have ultrathin structures with atomic thickness,and their unique photoelectric properties have attracted extensive attention from researchers in the fields of physics,chemistry,biology and materials.Different two-dimensional materials can be combined to form lateral or vertical van der Waals heterojunction.The two-dimensional van der Waals interlayer forces to a certain extent determine the photoelectric response performance of heterojunction devices,further expanding the potential application of two-dimensional materials in the field of optoelectronics.When stacking heterojunctions manually,the process of mechanical stripping and transfer introduces polymer residues,which will affect the photoelectric response of two-dimensional heterojunctions.In this paper,spatial domain limiting and one-step chemical vapor deposition assisted by molten salt were used to obtain a two-dimensional vertical MoSe₂/WSe₂ heterostructure.Raman imaging showed that the obtained MoSe₂/WSe₂ developed a vertical heterostructure.We also studied the photoelectric performance of MoSe₂/WSe₂ heterojunction devices,and the major findings are as follows:（1）High quality and ultra-thin vertical molybdenum diselenide/tungsten diselenide heterojunction was prepared on SiO₂/Si substrate by one-step chemical vapor deposition method.The effects of growth temperature,growth time,carrier gas inlet time,carrier gas flow rate and other process parameters on the quality of heterojunction were analyzed.At a heating rate of 20℃/min,it was heated to 780℃and naturally cooled to room temperature to obtain vertical MoSe₂/WSe₂ two-dimensional material heterostructures.H₂/Ar carrier gas began to enter at 700℃with a flow rate of 80 sccm.（2）Atomic force microscopy showed that the thickness of MoSe₂ and WSe₂ were both 1.5 nm.Raman imaging was conducted on A_1gof MoSe₂ and E_2g¹ of WSe₂.The results showed that these two vibration modes were observed simultaneously in an area,indicating that MoSe₂ and WSe₂ form vertical heterojunctions on the two-dimensional material.（3）PL spectral tests show that the band gap widths of MoSe₂ and WSe₂ are 1.51e V and 1.59 e V,respectively.In the experiment of variable temperature Raman spectroscopy,the vibration frequencies of A_1g（Se-Mo）of MoSe₂and A_1g（Se-W）and E_2g（Se-W）of WSe₂ moved toward low frequency with increasing temperature.In the variable temperature PL spectroscopy experiment,it was observed that the intramural exciton energy of MoSe₂ and WSe₂ decreased with increasing temperature.Kelvin probe force microscopy study showed that the surface potential difference between MoSe₂ and MoSe₂/WSe₂ heterojunction is about 100 m V in the MoSe₂/WSe₂heterojunction.（4）The output characteristic curve of MoSe₂/WSe₂ heterojunction device shows that the heterojunction device has certain rectification characteristics with a rectification ratio of about 100.Under the irradiation of 638 nm laser,the MoSe₂/WSe₂heterostructure device has an optical response time of 28μs,a response time of 20 A/W,and a detection rate of 4.5×10¹³Jones.At the same time,the MoSe₂/WSe₂heterojunction device can detect light at 940 nm.