Density functional theory calculations of helium clustering in mono-, di-, and hexa-vacancy in silicon

摘要

Combining classical molecular dynamics and first-principles DFT calculations, we perfom an extensive investigation of low energy configurations for He_nV_m complexes in silicon. The optimal helium fillings are hence determined for V_1, V_2, and V_6 (figure on the right), and the structures formed by helium atoms arrangements in the vacancy defect are analyzed. For V_1 and V_2, the He atoms structure is mainly controled by the host silicon matrix, whereas a high density helium packing is obtained for V_6. For the latter, we estimate a helium density of about 170 He nm~(-3) in the center of the hexa-vacancy at the optimal helium filling. Relaxed structures obtained from DFT calculations for configurations with the lowest formation energies: (a) He_(14)V_1, (b) He_(20)V_2. and (c) He_(40)V_6.