| The radiation environment in space is composed of complex mixed particles,and neutrons play a very important role in the radiation of particles in space.Silicon carbide(SiC),as the third generation semiconductor,has the advantages of large band gap,high thermal conductivity,fast electron saturation drift,high critical breakdown field strength and strong radiation resistance,so the nuclear radiation detector prepared by silicon carbide has the characteristics of small size,high temperature and high pressure resistance,and can work in the environment of large radiation flux.At the same time,because of the large thickness of the sensitive region,the PIN device can withstand higher radiation intensity and higher reverse bias voltage.Therefore,the 4H-SiC PIN junction device is designed and fabricated in this paper,and the main research work is as follows.In this paper,we choose the structure of the high resistivity SiC epitaxial layer with 20?m and carrier concentration 1014cm-3 epitaxial layer on 360?m low resistivity SiC single crystal as the substrate.After B2O3 was coated on the substrate surface by evaporation solvent method,the samples were treated by step heat treatment at 650?(30min)-1250?(60min)-1450?(30min)(hereinafter referred to as 1250?)and 650?(30min)-1450?(60min)-1450?(30min)(hereinafter referred to as 1450?)in oxygen atmosphere.Firstly,the removal of residual boron oxide on the surface of the sample after B diffusion doping was studied.Through the analysis of metallographic microscope,it is found that there are still granular residues on the substrate surface after chemical cleaning,and the surface residues are basically removed after mechanical polishing.Energy spectrum analysis shows that the surface composition of mechanical polishing is B4C.The experimental results show that mechanical polishing is more effective than chemical cleaning on the removal of residual boron oxide on the surface.Secondly,the composition and morphology of the samples annealed at 1250?and 1450? were studied.The atomic ratios of B,C and Si in the samples were analyzed by EDS energy dispersion.it was found that for the samples at 1250? and 1450?,about 23.1%and 25.7%of the diffused B atoms were used for SiC doping,and about 76.9%and 74.3%B existed on the sample surface in the form of B4C,but the local oxidation on the surface of the sample at 1450? was relatively obvious.Using the resistivity measured by Vanderbilt method,the carrier concentration of the diffusion doping layer in the sample at 1250? is calculated to be 1.04×1016cm-3.By observing the surface of the sample by SEM,it is found that the area of poor conductivity increases and the surface state of the sample degrades when annealed at 1450?.Finally,the Al/Ti/Au ohmic electrode was prepared on both sides of the sample at 1250? and 1450? by thermal evaporation,and the electrical properties of the device were characterized.In order to compare and illustrate,the Ni/Au Schottky device is fabricated from the sample without boron diffusion treatment.The turn-on voltage of the Schottky device is 1.4V,and the leakage current density is 1.86×10-10A/cm2 and the ideal factor is 1.19 at-50V.For the device fabricated at 1250?,the turn-on voltage is 2.1V,the leakage current density is 8.29×10-7 A/cm2 and the ideal factor is 1.28 at-50V.Compared with the IV characteristics of Schottky devices without B diffusion,the turn-on voltage of H31 devices is closer to the theoretical value of PIN devices.Combined with the results of resistivity measurement by Vanderbilt method,it is considered that the preparation of P-type SiC layer is realized in this experiment,and then silicon carbide PIN devices are fabricated.For the device fabricated at 1450?,the turn-on voltage is 1.25V,the leakage current density is 7.87×10-4A/cm2 at-50V,and the ideal factor is 2.04 and 8.84,respectively.Compared with the device prepared at 1250?,the electrical performance of the device is degraded,which is mainly due to too many defects caused by long-time annealing at higher temperature. |
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