  The influence of disorder, both structural (non-diagonal) and on-site
(diagonal), is studied through the inhomogeneous Bogoliubov-de Gennes (BdG)
theory in narrow-band disordered superconductors with a view towards
understanding superconductivity in boron doped diamond (BDD) and boron- doped
nanocrystalline diamond (BNCD) films. We employ the attractive Hubbard model
within the mean field approximation, including the Coulomb interaction between
holes in the narrow acceptor band. We study substitutional boron incorporation
in a triangular lattice, with disorder in the form of random potential
fluctuations at the boron sites. The role of structural disorder was studied
through non-uniform variation of the tight-binding coupling parameter where,
following ex- perimental findings, we incorporate the concurrent increase in
structural disorder with increasing boron concentration. We illustrate stark
differences between the effects of structural and on-site disorder and show
that structural disorder has a much greater effect on the density of states,
mean pairing amplitude and superfluid density than on-site potential disorder.
We show that structural disorder can increase the mean pairing amplitude while
the spectral gap in the density of states decreases with states eventually
appearing within the spectral gap for high levels of disorder. This study
illustrates how the effects of structural disorder can explain some of the
features found in superconducting BDD and BNCD films such as a tendency towards
saturation of the T_{c} with boron doping and deviations from the expected BCS
theory in the temperature dependence of the pairing amplitude and spectral gap.
