Preparation And Optoelectronic Properties Of Gallium Tellurium Two-Dimensional Materials And Heterojunctions

Currently,responsivities of commercial photodetectors based on traditional semiconductor materials,such as silicon,gallium nitride and indium gallium arsenide,are less than 1 A/W,which makes them difficult to meet future needs.Unlike other two-dimensional materials such as graphene,bulk GaTe has a 1.7 eV p-type direct band gap at room temperature,which leads it to possessing a large light absorption coefficient.It is obvious that GaTe is possible to achieve high responsivity in the range from near infrared to visible light.Besides,large-area and high-quality preparation with controllable thickness is the key to the practical application of GaTe two-dimensional materials.However,the two-dimensional GaTe reported by other papers are generally prepared by mechanical exfoliation or physical vapor deposition.The size of two-dimensional GaTe prepared by the above methods is too small and the process of preparation is not easy to control.Aiming at the above problems,our work focus on using chemical vapor deposition to prepare high-quality GaTe nanosheets with large area and thin thickness.Further more,metal electrodes were deposited using a shadow mask to prepare photodetectors based on GaTe two-dimensional materials.Finally,in order to further improve the performance of photodetectors,we constructed a GaTe/MoSe₂ P-N heterojunction.At first,we used Te powder as the tellurium source and Ga liquid as the gallium source,two-dimensional GaTe material was prepared by chemical vapor deposition（CVD）.The research results show when reaction temperature is 650 ℃,distance between two precursors is 16.5 cm and growth time is 12 min,we successfully prepared a monolayer（0.8 nm）GaTe on a mica substrate.Monolayer GaTe nanosheets have a maximum size of approximately 150 μm.In addition,the surface morphology and structural properties of the prepared GaTe nanosheets were researched,and it was verified that the prepared GaTe is a single crystal material with high quality.On this foundation,the photodetector constructed based on the prepared few layer GaTe has good photoelectric performance.Under the illumination of 360 nm monochromatic light with illumination intensity of 1.51 mWcm^-2,the highest responsity is 66.29 AW^-1,the highest detectivity is 1.34× 1010 Jones.Under the bias voltage is 5V,the response time is160 ms,and the response is symmetrical.Then,we used Se powder as the selenium source and MoO₃ as the molybdenum source,two-dimensional MoSe₂ material was prepared by chemical vapor deposition（CVD）.When reaction temperature is 850 ℃,growth time is 25 min,air flow rate is105 sccm,and hydrogen ratio is 25%,we successfully prepared a large-size monolayer MoSe₂ on 300 nm Si/Si O2.The carrier mobility and on/off ratio of transistor based onthe prepared monolayer MoSe₂ is respectively 17 cm²V^-1S^-1 and 106,which is equivalent to the performance of a transistor prepared by monolayer MoSe₂ with mechanical exfoliation.It shows that the large-area MoSe₂ we prepared has high quality and can be used as a suitable N-type material to form heterojunctions with GaTe.At last,the GaTe/MoSe₂ vertical heterojunction was prepared by a two-step CVD method.However,due to the problem of lattice adaptation,the crystallization of the heterojunction prepared by the above method is poor.Instead,a PMMA-assisted transfer method was used to construct a GaTe/MoSe₂ vertical heterojunction,and it was successfully applied to photodetectors.Under the illumination of 360 nm monochromatic light with illumination intensity of 1.51 mWcm^-2,the highest responsity is 671.52 AW^-1,the highest detectivity is 1.48×1010 Jones.Under the bias voltage is 10 V,the rise time is 46 ms,and the decay time is 74 ms.Compare to the two-dimension GaTe,GaTe/MoSe₂ heterojunction responsivity raises 10 times,and the detectivety also raises 1.1 times.The rise time is reduced by 114 ms and the decay time is reduced by 86 ms.The excellent performance of GaTe/MoSe₂ heterojunctions is derived from the built-in electric field of the PN junction,which can increase the hole-electron separation efficiency.On the other hand,it is attributed to the direct band gap type,high surface area,and two-dimensional characteristics of the material.This unique property facilitates the absorption of photons and the separation of photogenerated electron-holes.Photodetectors based on photovoltaic GaTe/MoSe₂ P-N heterojunctions have achieved ultra-high and ultra-fast detection in the visible light field,and have good application prospects in photoelectric sensing.