Positional dependence of optical absorption in silicon nanostructure

We present a theoretical study of the optical absorption process of a 9×9 Si quantum wire. We calculate the imaginary part of the dielectric constant ε2 and the contribution to ε2 due to three Si atoms located in different positions using the non-orthogonal tight-binding method. From these calculations, we clearly find for the first time that the optical absorption below 3.4 eV tends to occur in the inner region of the 9×9 Si quantum wire.