Characterization Of Vacancy Defect Cluster In Crystal Silicon

The behavior and the parameters of trivacancy(V3)cluster defects in silicon such as the formation energy,transition levels and migration energy are investigated in this work by using first principle(DFT)methods of calculation.Also,the calculation is undone for defects with various charged states.The values of transition levels and migration energy of defects then are obtained by experiments and used to verify the accuracy of the calculation.The calculation are carried out by using VASP software employing Heyd-Scuseria-Ernzerh(HSE)screened hybrid functional potential that helps overcome the deficiency in predicting band gaps.The results has shown that V3 is bistable in the neutral charge state with the fourfold coordinated configuration(FCC)being lower in energy than the planar hexagonal ring configuration(PHR).However,the calculation shows that for charged supercells the most stable form was the planar hexagonal ring(PHR)configuration.The results suggest that trivacancy V3 is bistable defect with different configurations.Next,the electronic structure of these complex defects is investigated by inspection of their transition levels.For the ionization energies of V3[PHR] we obtain the first and the second donor transition levels,and the first and the second acceptors energy levels.For the ionization energies of V3[FFC] the first acceptor level is obtained.It is found that despite V3[PHR] having deep donor and acceptor levels,in equilibrium the defect will be in the neutral FFC state for a wide range of Fermi energies.Formation energies of neutral FFC trivacancies are 6.5 eV.If the Fermi level is near the band edges,V3 is predicted to occur in the PHR form in the double plus or double minus charge states.The transformation mechanism of V3 [PHR] to V3 [FFC] and migration mechanism of trivacacy are investigated.The respective minimum energy migration paths is obtained from CI-NEB calculations.Hence,the results show that the migration energy for neutral trivacancy(2.50 eV)is higher than the transformation energy needed for the process V3[PHR] → V3[FFC](1.40 eV).The same is true for trivacancies in different charge states.Therefore,it is expected that first the transformation process would be taken place with increasing temperature,until temperature reaches the value when the migration process would be dominated.In order to verify the obtained theoretical and calculated results the NPN 2N2222 transistors are irradiated with high-energy particles and subsequent measurements of electric characteristics of defects are carried out.The behavior of the radiation-induced defects is experimentally characterized by deep level transient spectroscopy(DLTS)after the irradiation and the post irradiation anneali ng.All experimentally obtained transitions levels are in good agreement with calculated values.The behavior of trivacancies with annealing temperatures also agrees well with predicted one by calculation.