Study On Perparation Technology And Photoelectric Preformance Of Single-Layer WS₂ Crystal Film By CVD

As a representative of two-dimensional materials,graphene has aroused extensive attention due to its excellent optical and electrical properties in recent years.As one of the two-dimensional materials,WS₂inherits the advantages of high carrier mobility and flexibility of graphene.In addition,It possess the wide-band-gap structure what graphene lacks.When the bulk material of WS₂becomes monolayer,its indirect band gap is able to change into direct band gap,which shows good optoelectronic performance,so it has an important application value in photodetectors,sensors and other fields.However,the research of WS₂crystal thin film is just at the beginning stage,the key and difficult points are still the controllable preparation of WS₂crystal thin film and the construction of devices.In this paper,the author systematically conducted study on the preparation of WS₂crystal thin film,the construction of single-layer WS₂crystal thin film photodetectors and the device performance under different conditions,made a conclusion of a complete experimental system from material growth to performance research,which created conditions for the development of WS₂high-performance photodetectors.The main results were as follows:?1?In this paper,the chemical vapor deposition?CVD?method was used to make controllable preparation of single-layer WS₂crystal thin film.The effect of different growth conditions on the growth of WS₂crystal thin film was studied and the growth mechanism was explored.The results reflected that WO₃heating temperature,substrate temperature,reaction time,carrier gas flow rate,raw material ratio and growth distance had the most obvious impact on the growth of WS₂crystal thin film.Under the conditions of 1020?heating temperature,870?growth temperature,reaction time of 20 min,carrier gas flow rate of 140 sccm,0.1 g of WO₃and 1 g of S powder,and growth distance of 10 cm,the single-layer WS₂thin film with high quality,large size and regular morphology were prepared.?2?Through the study of the preparation technology of single-layer WS₂crystal thin film photodetector,one-step and two-step methods for the preparation of photodetectors were obtained.The results reflected that the one-step method,which directly used the growth substrate as the device substrate,had the advantages of simple process and short experimental period.However,this method could not make full use of WS₂film,and it was able to damage the film and affect the performance of the device.The electrodes of photodetectors were fabricated on the new substrate by two processes of photolithographic mask and hard mask,and the thin films on the growth substrate were transferred to the new device substrate.When using the two-step method to prepare photodetectors,it was concluded that the bonding force between the metal electrode and the substrate prepared by the hard mask method was insufficient,which was easy to damage the devices.However,the two-step method of fabricating photodetector electrode by photolithography mask and completely transferring the thin film to the new device substrate by location transfer method had the advantages of high accuracy and strong controllability,which was the best preparation process of photodetector.?3?Through the study of the performance of single-layer WS₂crystal thin film photodetector,the law of photoelectric performance of device under different illumination,external voltage and wavelength.The results reflected that under different illumination,the photocurrent enhanced with the increase of illumination,while the responsivity of light and the normalized detectivity decreased obviously.Through the study of the performance parameters of the device at different wavelengths,it was found that the device has high photocurrent,responsivity of light and normalized detectivity at the incident wavelength of 405 nm,which showed that the single-layer WS₂crystal thin film photodetector had good light absorption near waveband of 405 nm,and has strong photoelectric conversion ability.With the enhancement of the external bias voltage at both ends of the electrode,the photocurrent,the responsivity of light and the normalized detectivity all increased,which indicated that the increase of the voltage during the operation of the device was helpful to improve the performance of the photodetector.