Two-dimensional Ga Te Crystal: Controllable Synthesis And Optoelectronic Properties Study

The photodetector plays an important role in electronic industry,which converts optical signals into measurable electrical signals.Therefore,it has a wide range of applications in optical communication,environmental monitoring,digital camera and other fields.Currently,with the rapid development and the increasing demand for semiconductor manufacturing technology,optoelectronic devices tend to be micro-sized,integrated,and flexible.Meantime,the traditional semiconductors,for instance Si,meet restrictions due to its physical properties and manufacturing costs,indicating the coming collapse of the Moore’s Law.Two dimensional(2D)materials have drawn the attention of scientists due to their unique physical and chemical properties,such as atomic level thickness,high mechanical flexibility,quantum effects,etc.In the 2D materials family reported to date,gallium telluride(Ga Te)is a rare p-type semiconductor with a thickness-dependent direct band gap of 1.65 e V and long carrier lifetime of 2.03 μs.Therefore,Ga Te has emerged as a potential candidate for photonics and electronics applications.Based on above background,this thesis is mainly focused on the basic study of inherent electronic/optic properties in 2D Ga Te and its potential application in photodetection,combined with related strategies for improving its profermance in photodetection.Besides,phase-selective fabrication of monoclinic and hexagonal 2D Ga Te by physical vapor deposition has also been achieved,and the latter one was synthesized for the first time.This thesis contains following conclusions:To address the challenge of controllable fabrication requirement in 2D Ga Te research,we developed a temperature dependent physical vapor deposition method(PVD)to achieve the selective synthesis of monoclinic and hexagonal phases for Ga Te nanosheets on mica substrate.Moreover,the hexagonal phases Ga Te nanosheets can be converted into monoclinic phases under fs-laser irradiation at ambient environment.To address the problem of low photo-absorption in ultrathin 2D Ga Te for photodetection,we designed and fabricated a vertical heterostructure consisting of Au nanoparticle(NPs)array on top of 2D Ga Te nanoflake.Taking advantage of the surface plasmon resonance enhancement of Au NPs array,the photo absorption of heterostructure is significantly improved by 5 times compared to pure 2D Ga Te,which thus effectively enhanced the key performance parameters such as responsivity,detectivity,etc.To address the problem of high schottky barrier induced by poor-quality metalsemiconductor(M-S)interfaces in 2D Ga Te for photodetection,we introduced pre-design and tranferable Au electrodes pattern to directly contact with mechanical exfoliated 2D Ga Te.Such a strategy can avoid straight thermal deposition of Au electrodes onto 2D Ga Te thus these defects or destructions induced by conventional method is absent here,resulting in high-quality M-S interfaces.The Schottky barrier is reduced so that mobility and photoelectric response performance are increased for the photodetector with transferred electrode.