Research On Deep Ultraviolet Photodetectors Based On Hexagonal Boron Nitride With MSM Structure

A deep ualtraviolet(DUV)photodetector is a research hotspot in the field of photoelectric detection technology,which has important applications and urgent demands in the fields of UV guidance,UV early warning,space communication,aerospace and UV astronomy.As a novel ultra-wide bandgap semiconductor,hexagonal boron nitride(h BN)whose bandgap is about 6.0 e V is one of the prefered materials for DUV photodetectors because of its excellent thermal and chemical stability,very large absorption coefficient(~ 7×105 cm-1),high dielectric strength(8 MV/cm)and other advantages.At present,the research of DUV h BN photodetectors is in the ascendant.Limited by the poor crystalline quality and simple structure design,the performance of DUV h BN photodetectors is unsatisfactory and needs to be improved.Therefore,in this dissertation,the DUV h BN photodetector with a MSM structure is studied from two aspects: improving the quality of h BN film and designing the device structure.The main research results are as follows:1.h BN films were grown on sapphire substrate at 1200? by low pressure chemical vapor deposition(LPCVD).The XRD peak of h BN(002)is 26.47 ° and the full width at half maximum(FWHM)is 1.28 °.The optical bandgap of h BN films is about 5.95 e V,the intrinsic absorption edge is about 208 nm,and the absorption coefficient near the absorption edge is more than 8.5 × 104 cm-1.Based on the prepared h BN film,a photodetector with a conventional MSM configuration was developed.The dark current density is less than 53 p A/cm2 and the detection cutoff wavelength is less than 224 nm at 20 V bias.The photocurrent produced by UV enhanced xenon lamp increases linearly with the increase of applied bias,and the photocurrent is about 3.12 n A at 20 V,and the ratio of photocurrent to dark current is larger than 312.2.In order to improve the quality of h BN films,a h BN buffer layer was grown on sapphire substrate at low temperature,and then h BN films were grown at 1350 ?.The surface of the prepared h BN film is very smooth and flat,and the XRD peak of h BN(002)planes is 26.56 ° and the FWHM is about 0.78 °.Based on the prepeared h BN film,a DUV photodetector with a conventional MSM structure has been manufactured.The dark current density is less than 53 p A/cm2 at 20 V bias,and the detection cutoff wavelength is less than 224 nm.The photocurrent produced by UV enhanced xenon lamp also increases linearly with the applied bias,which is about 29.8 n A at 20 V,and the ratio of photocurrent to dark current is more than 2980.3.The buried MSM electrode structure is proposed,and the effect of the buried MSM electrode structure on improving the performance of DUV h BN photodetector is analyzed qualitatively.A DUV h BN photodetector with a buried MSM structure was fabricated by RF magnetron sputtering,whose dark current density is less than 53 p A/cm2 under 100 V bias,and the detection cutoff wavelength is less than 224 nm.With the irradiation of UV enhanced xenon lamp,the photocurrent increases linearly with the applied bias,and the maximum photocurrent is about 32.7 at 100 V,and the ratio of photocurrent to dark current is larger than 3270,which proves the feasibility of the buried MSM electrode configuration.4.High quality h BN films were prepared on the transition metal of tungsten by high temperature LPCVD technology.During the growth process,tungsten films did not react with the reaction source and h BN,and still maintained good conductivity,and whose sheet resistance decreased to 0.8 ?/?.So,it proved that the transition metal of tungsten can be used as the buried MSM electrode for the DUV h BN photodetectors prepared at high temperature.The research ideas and results proposed in this dissertation have significance for improving the performance of DUV h BN photodetectors.The buried MSM structure is not only suitable for h BN photodetectors,but also has important reference value for photodetectors based on other materials.