Preparation Of InSe And In₂Se₃ Few Layers And Fabrication Of Device Electrodes By Transfer Printing Method

Two-dimensional III-VI semiconductors are new two-dimensional materials which have emerged in recent years.They can exhibit significant anisotropy due to their low symmetry of the lattice structure.Moreover,the interaction between the layers of these materials is higher than conventional TMD materials,leading to a phenomenon that the band gap and the band type can be changed remarkably with the number of layers.In addition,in virtue of the small effective mass and high mobility of the carriers as well as the large absorption coefficient for the materials,they have a great prospect for the applications in field effect transistors,wide-spectrum photodetectors and solar cells.The electrode is a crucial part to ensure the performance of device.It is well known that the transfer printing method(TPM)is one of the strategies for preparing the electrode.Actually,TPM refers to the processes by preparing electrodes onto an intermediate substrate firstly,and then transferring the electrodes from the intermediate substrate to the target samples.The method has many advantages including a clear interface between the sample and the electrodes,easy combination with electron beam lithography,and high-precision electrode pattern.Therefore,TPM is a simple and efficient electrode preparing method,having great potential application in electrodes preparation for the devices based on two-dimensional materials.This dissertation concentrates on the preparation of few layers of InSe and In2Se3 and the fabrication of device electrodes by TPM.It contains four chapters totally,and the contents of chapters are briefly described below.In the first chapter,we reviewed the origination and development of two-dimensional materials and methods for fabrication of electrodes.Specially,we introduced the structure,properties,applications and preparation methods for two-dimensional InSe and In2Se3 briefly.Finally,the developments and improvements in the preparation of electrodes by transfer printing methods were presented.In the second chapter,we first aimed to grow fewer layers of InSe through physical vapor deposition using InSe as the growth source,and we discussed the effects of several growth conditions on the growth results.However,systematic characterizations revealed that the as-grown product was actually few layers of In2Se3,and the underlying reasons were contributed to the surface oxidation of InSe source.By changing the source to In2Se3 and further improving the experimental conditions,few layers of In2Se3 with more regular shape,more uniform thickness and larger size were obtained.In the third chapter,the principles,process and equipment to prepare electrodes by transfer printing method were first introduced,and then the results of fabricated conventional electrodes and the electrodes with very narrow channel were demonstrated.The advantages and disadvantages of the method were discussed in detail.Furthermore,the reproducibility of the method and the electrodes spacing influenced by the transfer process were investigated.Finally,the prototype FETs and photo detectors based on few layers of InSe nanosheets were successfully fabricated,in which the electrodes were prepared by the transfer printing method.The excellent I-V character and photoresponse of the devices were also demonstrated.In the fourth chapter,we prospected for the opportunities and challenges of two-dimensional InSe and In2Se3 materials,and predicted potential applications of electrodes prepared by the transfer printing method.