The Study Of Radiation Effect Of Semiconductor Electronic Materials

Electronic materials are the basis of the modern electronic industry,and semiconductor materials that are regarded as an important component of electronic materials such as Si,Ge,GaAs and AlAs play a vital role in the modern society.Meanwhile,towards other critical applications such as aerospace,astronomy and nuclear-related areas,these semiconductors are exposed to different radiation environments,i.e.,X-ray,neutrons,electrons,ions,etc.,which may result in the generation of defects containing vacancies,interstitials,antisites and complex of these and even the degradation of the semiconductor's performance.Therefore,it is of great importance to study the radiation damage effects of semiconductor materials under the radiation environment and propose some strategies to improve their radiation resistance.Firstly,we employed an ab initio molecular dynamics(AIMD)method to explore the radiation damage effects of Si,Ge and Si/Ge superlattice(SL)under low-energy electron irradiation.It is found that the threshold displacement energies(E_ds)show a significant dependence on the recoil directions and the primary knock-on atoms(PKAs).As for bulk Si and Ge,the PKAs are more difficult to be dispalceed to form the point defects along the[110]direction,whereas in Si/Ge SL the Si atoms are more difficult to leave its initial site along the[111]direction and Ge atoms are more difficult to form defects along the[110]direction.Besides,the radiation resistance of the Ge atoms that are around the interface of Si/Ge SL is comparable to bulk Ge,whereas the Si atoms around the interface are more difficult to be displaced than the bulk Si,showing enhanced radiation tolerance of SL structure as compared with the bulk Si.Defect formation and migration calculations show that in the bulk structure the point defects are much easier to form,and the vacancies are more mobile,which may lead to the degradation in their properties such as volume swelling,decrease of density and toughness,resulting in the weakening radiation resistance of bulk structures.Secondly,the radiation damage effects of GaAs,AlAs and GaAs/Al(Ga)As SL have been explored using the AIMD method and some strategies to improve their radiation resistance have been also proposed.It is found that the atoms in AlAs are more difficult to be displaced than those in GaAs.As for the GaAs/AlAs SL,the Ga and Al atoms are more susceptible to radiation than those in the bulk AlAs and GaAs,whereas the As atoms need comparable or much larger energies to be permanently displaced from their lattice sites than those in the bulk states.Besides,we find that the antisite defects have slight effects on the SL's electronic structures,while a significant reduction of band gap or induced metallicity is found in GaAs/AlAs SL with the interstitial or vacancy defects.Further calculations show that the interstitial and vacancy defects reduce the electron mobility significantly,while the antisite defects have relatively smaller influences.Meanwhile,the AIMD simulations also confirm the experimental observation that the radiation resistance of GaAs/AlAs SL is enhanced by the introduction of Ga to the AlAs layer.The calculated potential energy increases for defect generation in GaAs/Al GaAs SL are found to be comparable and even higher than those in GaAs/AlAs SL,indicative of higher energy barrier for further defect generation,which results in enhanced radiation tolerance of GaAs/Al GaAs SL.Moreover,in the temperature range from 300 to 1200 K,the E_ds of GaAs/AlAs and GaAs/Al GaAs SLs are not sensetative to the temperature.Especially,there are generally more defects in the GaAs/AlAs SL at higher radiation energies,whereas the associated defects in the GaAs/Al GaAs SL generally remain unchanged.Thirdly,for the responses of 3C-Si C to low-energy electron irradiation have been explored using the AIMD simulations and are compared with radiation damage effect of Ti C and Zr C.It is found that C displacements are dominant in the cascade events of 3C-Si C,Ti C and Zr C.The associated defects in 3C-Si C are mainly FPs and antisite defects,whereas damage end states in Ti C and Zr C generally consist of FPs and very few antisite defects are created.The different radiation behaviors of 3C-Si C and transition metal carbide(Ti C and Zr C)can be originated from their different electronic structures,i.e.,the<Ti-C>and<Zr-C>bonds are a mixture of covalent,metallic,and ionic character,whereas the<Si-C>bond is mainly covalent.Besides,the AIMD results reveal that the C and Si atoms in 3C-Si C around the interface of stacking faults(SFs)in 3C-Si C are generally more difficult to be displaced than those in unfaulted 3C-Si C,indicative of enhanced radiation tolerance caused by the introduction of SFs,which agrees well with the recent experiment.The calculated potential energy increases for defect generation in3C-Si C with intrinsic and extrinsic SFs are found to be higher than those in unfaulted 3C-Si C,due to the stronger screen-Coulomb interaction between the primary knock-on atoms and their neighbors.In summary,the radiation damage effects of semiconductor materials are explored systematically in this study.It is shown that the E_ds of 3C-Si C are obviously larger than those for the first-and second-generation semiconductor materials,indicating that 3C-Si C may be more suitable for various electronic devices under radiation environment.Besides,for the above semiconductor materials,we also propose some strategies to improve their radiation resistance.As for bulk Si and Ge,the Si/Ge SL shows the enhanced radiation resistance.For GaAs/AlAs SL,its radiation resistance is enhanced by the introduction of Ga to the AlAs layer.For 3C-Si C,the introduction of stacking faults can significantly improve its radiation resistance.The presented results provide a fundamental insight into the underlying mechanism of displacement events in electronic materials and will help to advance the understanding of the radiation response of these widely-used materials.