Fabrication And Device Properties Of Bismuth Oxyselenide Crystals

At present,the development of silicon-based chip technology has gradually entered a bottleneck period,and the logic density is gradually approaching the physical limit.Due to the limitation of short channel effect and micro nano processing technology,the limit of"Moore’s law"has attracted extensive attention.It is of great significance to explore new channel materials and improve the performance of IC chips for the development of modern science and technology.Because of its unique and novel characteristics in optics,electronics,magnetism,two-dimensional materials have attracted widespread attention.In the practical application process of devices in life,the two-dimensional materials needed have controllable band gap,ultra-high mobility,simple preparation method,good environmental stability.However,the existing two-dimensional material systems（such as graphene,black phosphorus,TMDCs,indium selenide,etc.）can not meet these needs at the same time.Therefore,it is of great significance to explore new two-dimensional materials for the development of information technology.Bismuth selenoxides as a new two-dimensional material have attracted extensive exploration and attention.The growth and device properties of bismuth oxyselenide is systematically explored in this paper.The growth and performance of bismuth oxyselenide can be divided into three parts as follows:（1）Preparation and transport properties of high mobility Bi₂O₂Se single crystals.High performance Bi₂O₂Se single crystal with the size of 2 mm was prepared by melting method.The composition and morphology of Bi₂O₂Se single crystal were characterized and analyzed by micro Raman spectroscopy,X-ray diffractometer and energy dispersive X-ray spectrometer.All the characterization results show that the Bi₂O₂Se single crystal has ultra-high quality.Then,we measured the transport of Bi₂O₂Se single crystal in low temperature and strong magnetic field,and the samples showed good metallicity.Through the fitting analysis of the Sd H oscillation data,we can get the important physical information such as oscillation frequency,Fermi area,Fermi velocity,effective mass,Fermi surface position,relaxation time,carrier mean free path,and Sd H oscillation mobility 8192.4 cm²V^-1s^-1.The hall mobility of Bi₂O₂Se single crystal is more than 50000 cm²V^-1s^-1at low temperature,and the carrier concentration is 10¹⁹.By fitting the transmission timet_trand the quantum lifetimet_Q1of carriers,it is further proved that the high mobility of Bi₂O₂Se single crystal sample is due to the suppression of its backscattering.（2）Preparation and characterization of high quality Bi₂O₂Se nanosheets.We use the face-down CVD method to grow the Bi₂O₂Se nanosheets.Then,the growth mechanism of Bi₂O₂Se nanosheets was conjectured,and the process of forming Bi₂O₂Se nanosheets went through two steps:Bi₂O_3-xwas formed and deposited on the substrate in the reaction,and then reacted with Bi₂Se₃vapor to form Bi₂O₂Se nanosheets.Subsequently,it was found that increasing the growth rate can reduce the thickness of Bi₂O₂Se nanosheets and get thinner Bi₂O₂Se.We further studied the air stability of two-dimensional Bi₂O₂Se nanosheets,and found that the AFM images of Bi₂O₂Se nanosheets almost the same and the roughness did not change after 15 days or two months at room temperature,which proved that the samples had good environmental stability.（3）Preparation and transport properties of Bi₂O₂Se phototransistor.We have fabricated high-performance phototransistors based on high-quality Bi₂O₂Se nanosheets,which can achieve the whole spectral range of response from ultraviolet to communication band（300–1800 nm）,and the maximum response in ultraviolet band is 108696 A/W.In addition,the change trend of the maximum responsivity is consistent with the absorption trend,reaching the highest value in the ultraviolet band,and then decreasing gradually in the infrared band,and the responsivity decreases gradually.In the visible band,the response speed is very fast,the rising edge is only32ms,the falling edge is 98ms,and the bandwidth of-3d B is achieved at 5.4 k Hz.Through the spatial image of photocurrent in the infrared region was obtained by Bi₂O₂Se phototransistor,we can conclude that the generation of photocurrent is mainly attributed to the photovoltaic effect and photogating effect.In addition,our Bi₂O₂Se phototransistor has ultra-high sensitivity and has important applications in single point imaging.It can be used in ultraviolet,visible and infrared bands respectively,which lays a solid foundation for further practical application.