LUMINESCENCE IN POROUS SILICON - THE ROLE OF CONFINEMENT AND PASSIVATION

We perform the theoretical analysis of two wires of different size, si mulating porous Si, through the linear muffin tin orbitals method in t he atomic sphere approximation. We consider free, partially and totall y H-covered [001] Si quantum wires with rectangular cross section. We show that (a) quantum confinement originates the opening of the LDA ga p; (b) this opening is asymmetric: 1/3 of the widening is in the valen ce band, while 2/3 in the conduction band; (c) the near band gap state s originate from Si atoms located at the center of the wire; (d) the c onfinement is enhanced in the case of free surfaces; (e) the imaginary part of the dielectric function shows a low energy side structure str ongly anisotropic, identified as responsible of the luminescence trans ition; (f) the presence of dangling bonds destroys the luminescent pro perties.