Chemical Vapor Deposition Growth And Property Characterization Of Two-Dimensional Cr₂Te₃ Crystals

Due to the atomic-level thickness and many excellent properties,two-dimensional materials are expected to be used in the field of integrated circuits in the future.Since 2004,the successful preparation of graphene has set off a research boom in two-dimensional materials.However,due to the zero band gap of graphene,it cannot be used as a semiconductor material in the field of integrated circuits.Therefore,researchers have developed other twodimensional transition metal materials like MoS2,WS2,etc.Based on it,a variety of highperformance field effect transistors have been designed,which promotes the further development of two-dimensional materials.Since the Cr element is in the same family as Mo and W,it has similar physical and chemical properties,which is considered to be a suitable choice for the construction of high-performance electrical devices.However,due to the non-layered structure of chromium-based chalcogenides,which increases the difficulty of preparing single crystals,research at home and abroad still remains at the stage of material preparation.Therefore,based on the above research status,this paper successfully prepared ultra-thin two-dimensional Cr₂Te₃ samples by using the limited area chemical vapor deposition and two precursors:CrCl3 and Te.Moreover,we characterized and analyzed its structure,morphology and composition.Finally,we designed a field-effect transistor based on the material and studied its electrical and piezoelectric properties.This subject will provide new ideas for the preparation of two-dimensional Cr-based compounds,and also provide a certain basis for the study of piezoelectric properties and electrical properties of two-dimensional single crystal Cr₂Te₃.The work details are listed as follows:（1）Using a tube furnace with a single temperature zone,we have successfully prepared a two-dimensional material sample with a thickness of 10 nm on a mica substrate by the"limited area" chemical vapor deposition method under normal pressure conditions.And We explored the influence of growth time,temperature,carrier gas flow,precursor concentration,and substrate on material preparation.In addition,we discussed the "island-like" growth law of the two-dimensional Cr₂Te₃ material and summarized the preparation process parameters of the material.（2）Using microscope,SEM,and AFM,we have performed morphological characterization of the material,and it can be seen that the maximum size of the two-dimensional material is more than 100 μm and the thickness is as low as about 3 nm.Using XRD,TEM,XPS,etc.,we have analyzed the structure and composition of the material,which shows that the prepared material is a hexagonal Cr₂Te₃ material with uniform composition,good crystallinity and high quality.（3）Using Raman spectroscopy,we discussed the influence of different thickness,temperature,morphology,and substrate on the properties of the material,and it was found that the Raman peak shifted with the change of thickness and temperature.And we used it to study the environmental stability of the material.In addition,we tested the vertical piezoelectric effect of the material using a piezoelectric atomic force microscope and calculated its piezoelectric coefficient d33.（4）We explored the transfer technology of two-dimensional materials,and used the HFassisted transfer method to transfer the sample on the mica to the silicon oxide substrate.The back-gate field effect transistor based on two-dimensional Cr₂Te₃ material was fabricated by using maskless lithography machine,electron beam evaporation and other instruments.Electrical tests have shown that the material has good conductivity.We have studied the output and transfer characteristics of the device.It is found that the current is not sensitive to gate voltage regulation,which proves that the material exhibits typical metallic behavior.At the end of paper,we summarized our work and put forward the existing problems,then through analyzing the research status,we discussed the plans for future research.