Preparation And Photoelectric Properties Of WSe₂ Nanostructure Thin Films

Since the discovery of graphene,the research of 2D materials has attracted extensive attention.Especially,transition metal dichalcogenides(TMDs)semiconductors have shown great potential in the field of microelectronics because of their high carrier mobility,adjustable band gap and other excellent electrical properties.As an important member of TMDs family,pure-phase WSe₂ can be p-type or n-type along with good stability in air and excellent photoelectric properties.However,the scalable growth of high-quality 2D WSe₂thin films still remains a bottleneck to its mass application in micro electrical devices.Therefore,this thesis,targeting at WSe₂ thin films wafer-level growth,adopted the self-designed infrared-heating CVD method to carry out the systematic study on the controllable preparation of WSe₂nanostructure thin films and its photoelectric performance.The thesis includes the following main works:(i)The preparation of 1D WSe₂ nanocomposite films:In the presence of oxygen,by controlling the amount of selenium source,deposition time,reaction atmosphere among other conditions,a novel one-step method was successfully developed for the first time to grow aligned WSe₂-based 1D core-shell nanostructures on W or Si substrates.WSe₂ 1D nanostructures is composed of single-crystal W₁₈O₄₉ nanowire core and single-/few-layer WSe₂ shell.Their diameters are 20-60 nm and the lengths are in the range of 1-3?m.Furthermore,the uniform growth of the nanocomposite film on the 2-inch wafer substrate was achieved by upgrading the infrared heating CVD system.(ii)CVD growth of 2D WSe₂ thin films:using the same infrared heating CVD method but in hydrogen atmosphere,high-quality WSe₂ single-/few-layer continuous 2D films were prepared by optimizing the tungsten source,temperature,time and pressure.In this experiment,the samples were grown in low-pressure hydrogen atmosphere for 5 min,and the tungsten source was W-foils which was pre-oxidized at a high temperature in air.With the increase of oxidation time,WSe₂ had gradually grown from dispersed nanosheets to large-area continuous films.Finally,the continuous 2D thin film growth of single-/few-layer WSe₂ over 1 cm²-sized Si O₂ substrate was successfully achieved.(iii)Research on the photoelectric properties of WSe₂ 2D films:Selecting as-grown few-layer WSe₂ single crystal films as the photoelectric response materials,and the photodetectors with photosensitive area of only 1-4?m² were successfully prepared by micro-fabrications.The devices exhibited strong optical response in visible and near infrared bands,and the responsibility of a 10-layer WSe₂ device reached 0.2-0.4 A/W,showing the high-quality of as-prepared WSe₂ films.We expect this highly-efficient infrared heating CVD technology would be applicable to mass production of WSe₂ and other TMDs 2D materials.