Because of its chemical inertness, Helium can only form few compounds under radical conditions or some inclusion compounds (clathrates) that is stable under ambient conditions. By combining molecular dynamics (MD) and first principle calculation, we predict a new type of Silicon Helium inclusion compound with a well-defined stoichiometry under pressure: one Helium atom encapsulated in each cage formed by 12 Silicon atom that assume a hexagonal crystal framework. MD simulation reveals a spontaneous nucleation of the compound from the silicon melt mixed with helium gas under high temperature and pressure. The compound is found thermodynamically stable with respect to pure silicon and helium under mild pressure conditions. Density functional theory calculations further reveals that the Helium drastically changes the electronic structure of the host Silicon crystal due to its expelling the electronic charge density out of the silicon crystal interstitial sites. Remarkably, the change leads to an indirect to direct band gap transition in silicon, with a band gap size of 1.1 eV, both being key properties for application in a high efficiency solar cell.

Theory predition of a novel Si-He compound: Structure, property and synthesis

254th National Meeting (2017)

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