Published online by Cambridge University Press: 15 February 2011
We have studied the structural relaxation of vacancies in amorphous silicon (a-Si) using a tight-binding molecular-dynamics method. The most significant difference between vacancies in a-Si and those in crystalline silicon (c-Si) is that the deep gap states do not show up in a-Si. This difference is explained through the unusual behavior of the structural relaxation near the vacancies in a-Si, which enhances the sp2 + p bonding near the band edges. We have also observed that the vacancies do not migrate below 450 K although some of them can still be annihilated, particularly at high defect density due to large structural relaxation.