Surface states in P- and B-doped amorphous hydrogenated silicon

Abstract

The density of surface states, of $a$-Si: H films doped with B and P was inferred from the experimentally determined surface Fermi level ${E}_{\mathrm{SF}}$ and bulk Fermi level ${E}_{F}$. The films were prepared by rf plasma decomposition of Si${\mathrm{H}}_{4}$ doped with 0-2 vol% ${\mathrm{B}}_{2}$${\mathrm{H}}_{6}$ or 0-2 vol% P${\mathrm{H}}_{3}$. ${E}_{\mathrm{SF}}$ was determined from x-ray photoelectron spectroscopy measurements of the Si $2p$ core levels, and ${E}_{F}$ was inferred from the activation energy of the electrical conductivity. In the case of sputter-cleaned surfaces the density of surface states ${N}_{s}=10\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{eV}}^{\ensuremath{-}1}$ for $n$-type material and 13\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{eV}}^{\ensuremath{-}1}$ for $p$-type material; the bands are flat (${E}_{F}={E}_{\mathrm{SF}}$) when ${E}_{F}$ is 0.1 eV above midgap. In the case of oxidized surfaces ${N}_{s}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{eV}}^{\ensuremath{-}1}$ for $n$-type material and 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{eV}}^{\ensuremath{-}1}$ for $p$-type material; flat-band condition is satisfied when ${E}_{F}$ is 0.2 eV above midgap.