CVD Growth Of Large-area Monolayer H-bn And Research On MoTe₂/h-BN Heterojunction Thin Film Transistor Devices

Since Moore's Law was proposed in the 1960s,the number of components in electronic circuits has doubled every two years.So far,the volume and number of silicon-based transistors have reached the limit,as a result,the device performance is difficult to get further improvement.In order to extend Moore's Law,it is urgent to find alternative semiconductor materials.For some emerging transistors,such as Germanium,Indium Gallium Arsenide and Indium Phosphide transistors,the thickness of aboved semiconductor layers can be fabricated on nanoscale.However,the drifting of electrons in the channel layer is always hindered to a certain extent.Because the defects inevitably generated in the interior and the surface of the semiconductor materials during the growth process,which will have a great impact on the performance of the device.Transition metal dichalcogenides?TMDs?possess strict and unique two-dimensional layered structure.The isolated layer is comprised of transition metal element and chalcogen element through in-plane covalent or ionic bonds.The inter-layers are combined by weak van der Waals force.In addition,the electrical and optical properties of TMDs change dramatically when the thickness decreases from bulk to single layer.Mo Te₂is endowed with characteristics of most TMDs.Its single-layer 2H phase?hexagonal structure?possesses a direct band gap of 1.1 e V.The small difference of band gap between Mo Te₂and silicon?1.12 e V?makes it feasible alternative to silicon as semiconductor material in transistors.Moreover,Mo Te₂exhibits a small formation energy difference?<50 me V?between the 2H phase?semiconductivity?and the 1T'phase?metallic?^[1],which is viable for in phase engineering.This paper focus on the preparation of large-area continuous single-layer h-BN thin films as substrate material.After that,large-area Mo Te₂thin films were grown on as-fabricated h-BN substrate to improve the performance of Mo Te₂based thin-film transistors?TFTs?.H-BN has a strict single-layer structure without dangling bonds.Furthermore,it shows superior insulativity and phonon scattering shielding effect.Based on the above performance,h-BN can be used as a suitable substrate to improve the quality of Mo Te₂without affecting the gate dielectric of the Mo Te₂thin film transistor.The research is mainly composed of following three parts:?1?Preparation of single-crystal copper foil.It is easier to achieve the growth of large-area continuous h-BN thin film on?110?oriented copper foil due to its symmetry and lack of grain boundaries.After that,we investigated the effect of annealing temperature and cooling rate on the surface orientation of copper foil.?2?Preparation of monolayer h-BN thin films.Ammonia borane?NH₃BH₃?was used as a precursor to prepare monolayer h-BN thin films on single-crystal copper foil by chemical vapor deposition?CVD?.The effects of growth temperature and precursor temperature on the thin films were also studied.?3?growth of Mo Te₂and fabrication of TFT device.The large area growth of Mo Te₂on h-BN was achieved through molecular beam epitaxy technology.The obtained Mo Te₂/h-BN heterojunction was constructed into a thin film transistor and its electrical properties were evaluated.In conclusion,we analyzed the preferred orientation mechanism and successfully prepared?111?and?110?oriented single-crystal copper foils by optimizing the annealing process.Large-area continuous monolayers h-BN thin film was prepared on single-crystal copper foils by CVD.The growth of Large-area Mo Te₂thin film on single-layer h-BN was realized for the first time.After fabricating into a Hall device and a thin film transistor,we found that its Hall mobility and current on/off ratio were significantly improved compared to those of the devices made directly on Si O₂/Si substrate.The above work provides a new insight into the large-area growth of Mo Te₂thin films and paves a new way following the Moore's Law.