Simulation Of Displacement Damage In Semiconductor Detectors Of Space Environment Under Nesting Shields

A variety of spacecrafts and satellites were developed by scientists and engineers for exploration and investigation of space environment.The corresponding materials were also considered to investigate the influences of cosmic rays to spacecrafts.Guarantees for a series of complex aerospace engineering were provided at the same time,such as cosmic exploration,transportation,global positioning,communications,etc.The trapped protons and electrons,the galactic cosmic rays,the solar cosmic rays and others were included in the radiation of near-earth space environment.It contains a wide variety of charged particles with a wide range of energy,including protons,αparticles,sorts of heavy ions and mesons,high-energy electrons,and so on.For the outer components onboard spacecrafts,it will be damaged by the radiation environment,upon exposure.The main mechanisms of damage include the total ionizing dose effects,displacement damage and single event effects.For high-energy particles it’s easier to bring out the displacement damage.This may generate the Frenkel defect（vacancy-interstitial pairs）,induce the changes of the carrier concentration,to influence the electrical properties of the materials.The outer components onboard the spacecraft will produce a large number of secondary particles under the irradiation of cosmic rays at the same time.Except for the protons from cosmic rays,the secondary neutrons produced by the outer loads would make a considerable contribution to the displacement damage of the inner detectors.The influences from secondary particles are more obvious for the semiconductor detectors because of their sensitive properties.Therefore,it is essential to research the displacement damage caused by the secondary particles when considering the estimation of the lifetime of the spacecrafts and the degradation of electrical performance.A Monte Carlo code called Particle and Heavy Ion Transport Code（PHITS）is used in this paper to simulate the displacement damage from secondary particles to the semiconductor detectors under multi-layer nesting shields in the space.Taking the following X-ray telescope（FXT）in the Einstein Probe satellite（EP）as an example,the spectra of secondary particles that generated by the shields are obtained,and the displacement damage of semiconductors are simulated by the spectra mentioned.The results of simulation show that for the silicon detector onboard FXT,the athermal recombination corrected displacements per atom（arc-dpa）reached 83.515×10^-24/Source,and a large amount of displacement damage accumulation is produced in the incident depth range of 260～270μm.Furthermore,to consider the accumulation of displacement damage under the duration of exposure from 1 s to 10000 s,the results show that the total dose of displacement damage keeps increasing with the number of the projectiles.Two corresponding methods for quick estimation of the displacement damage in the detectors are summarized,based on the fact that the defect production efficiency and the dpa per projectile almost turn to invariant when the duration of exposure is long enough.To explore the details of the displacement damage accumulated at 260～270μm from the incident surface under the irradiation in 1 s,a molecular dynamics code named LAMMPS is used.The outcomes show that the displacement damage clusters are produced by the cascades.The same methods of simulation are used for Si C and Ga As,and the similar results are obtained.Because of the different properties of these materials,the depths for the accumulation of the displacement damage are different.Among these materials,the cumulate depth of Si C is the shallowest,the depth of Ga As is the deepest,the depth of Si is between them.