Research On The Stability Of Hexagonal Boron Nitride Films And Its Deep Ultraviolet Photodetectors With MSM Structure

Hexagonal Boron Nitride?hBN?,which is a syntheticultra-wide bandgap semiconductor material with a graphite-like structure,commonly known as"white graphite."Its bandgapis up to 6.0 e V or more,the corresponding intrinsic absorption edge is approximately 207 nm,the absorption coefficient is as high as 7×10⁵ cm^-1 near the absorption edge.Besides,it has extremely high thermal stability,chemical stability,and radiation resistance,and itsdielectric strength is up to 8 MV/cm.These excellent properties make it a preferred materialfor making deep ultraviolet?DUV?photodetectors.However,due to the limitations of the growth process,the preparation of high-quality,large-size hBN single crystals and epitaxial films still faces great challenges.The research of DUV photodetectors based on hBN thin films is still in its prototype stage,and the detectors generally have low responsivity.This paper focuses on the hydrolytic mechanism and growth process optimization of hBN thin films prepared by rf magnetron sputtering,the preparation and performance of DUV photodetectors based on hBN thin films.The main research contents and results are as follows:We deposited hBN thin films on silicon,sapphire and quartz substrates by rf magnetron sputtering,the chemical composition and structure of these films were analyzed by XPS.The results of XPS show that the atomic percentage of oxygen in the hBN thin films which were easily attacked by water vapor generally higher than30%,and those oxygen is mainly bonded with the boron atom,indicating that there are boron oxide present in the films.As boron oxide easily absorbs water vapor in the air thus generate boric acid,the films were easily attackedby water vapor.In order to control the oxygen content of the hBN film,the preparation process was optimized:?1?By sintering the target for more than 2 hours at a high temperature of 2000°C,the oxide in the target would be fully sublimed,thus the oxygen impurity in the hBN target would be removed.?2?Through baking the inner wall of the growth chamber and repeatedly introduced the high-purity nitrogen to purify the growth chamber,the oxygen-containing gas adsorbed in this chamber would be removed as much as possible.After optimization of the process,the oxygen content in the prepared hBN thin film is drastically reduced,and the stability of the hBN thin films is greatly improved,it can stably exist in the air without hydrolysis,even the hBN films were soaked into the deionized water,the properties of these films haven't significantly changed.The prototype of the DUV photodetector based on the stable hBN thin films with a metal-semiconductor-metal?MSM?coplanar interdigitated electrode structure was developed.The detector has a detection cut-off wavelength of 230 nm and a peak response wavelength of 200 nm.The maximum responsivity is 10mA/W.Due to the use of standard silicon detectors for calibration,the shortest calibration wavelength of a laboratory-built spectral response test system is only 200 nm.The spectral response curve below 200nm of hBN DUV photodetector needs further research.In addition,using hBN films as the intercalation layer,a kind of MSM-type DUV enhanced silicon photodetector was developed.In the wavelength range of 250-800nm,the response curve of this photodetector is basically the same as that of the ordinary silicon photodetector,and compared with the ordinary silicon photodetector,the responsivity of this DUV enhanced silicon photodetector is significantly improved in the wavelength range of 200-250 nm.