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A series of the formation energies Ef of boron dopants in Si quantum dots with different shapes, including tetrahedron (TH), tetrahedron-centered (TC), and octahedron (OT), are investigated by the first-principle calculation. The site of B dopants can be simply divided into vertex (“′v”), edge (“e”), and facet (“f”) on the surfaces of the Si quantum dots. It is found that the Ef value is strongly relying on quantum dot shape. In particular, when the size is given, one finds that TH shape has the lowest Ef values, while OT shape possesses the largest ones, and thus there is a sequence of Ef(TH) < Ef(TC) < Ef(OT). This can be well explained by the shape factor λ since the same sequence of λ(TH) < λ(TC) < λ(OT) exists. Interestingly, for each shape of TH, TC, and OT, λ is not a constant, behaving as the increasing trend when the size increases, while it behaves in decreasing trend for Ef. This means that the shape and the size have the opposite roles in Ef. Thus, considering the shape influence, one can say that the Si quantum dot with a smaller λ value is in favor of B dopants in them.

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