Growth Of Hexagonal Boron Nitride Thick Films As Deep Ultraviolet Photodetectors And Theoretical Calculations On Their Surface Functionalization

In recent years,hexagonal boron nitride(h-BN)has attracted intensive attention,because of its excellent physical and chemical properties,making its controlled preparation and applications highly desirable.There are various preparational processes for h-BN films,including chemical meteorological deposition(CVD)and physical meteorological deposition(PVD).So far,how to prepare large-area h-BN films with controllable thickness,structure,crystallinity and purity is a major challenge.Also,a high quality h-BN with ideal properties is the basis and guarantee for the next application and development.Therefore,in this thesis,we have carried on the growth of high-quality h-BN thick films for their applications as deep ultraviolet(DUV)photodetectors as well as the theoretical calculations on surface functionalization for gas interactivity improvement.1.Using argon and nitrogen as precursor gas,h-BN films with high quality and thickness were deposited directly on dielectric substrates by double ion beam assisted sputtering method at 500°C.The thickness of the as-prepared h-BN film varies with the time of deposition.The film thickness is about 50-500 nm,and when it reaches 500 nm,the film surface is still smooth and continuous without visible cracks and holes,indicating that the thickness of the film can continue to increase.The results of FTIR,XRD and Raman tests confirm the existence of pure h-BN.AFM further confirms that the thick h-BN film is flat and smooth with an RRMS=0.380 nm.2.Considering that h-BN is a wide band gap semiconductor with adjustable band gap,high temperature resistance and stable physical and chemical properties,it is the preferred material for fabricating DUV photodetectors that can be used in extreme environment.The performance of MSM type DUV photodetector based on h-BN thick film exhibits responses to the incident light of 204 nm with a responsivity of 0.5 AW-1.The cutoff wavelength is near 218 nm.These data demonstrate that h-BN thick films directly grown on quartz can be used as photodetectors in DUV spectral region with reliable stability and repeatability.In addition to the experimental exploration of possible applications,in this thesis,we have also investigated the functionalization of h-BN as well as their corresponding interaction with gas molecules based on first-principle calculations.S-and OHgroups have been used to decorate h-BN surface and/or edges,h-BN film exhibits significantly improved interactivity with NO2、CO2、CH4 gas molecule.Therefore,in this thesis,h-BN are studied from two aspects in name of experimental approaches and theoretical calculations,the results from which demonstrate the potential applications of h-BN films in photodetector,gas sensor and energy storage devices.