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

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 $N_s=10\mathrm{}\times {10}^{12}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$ for $n$-type material and 13×${10}^{12}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$ 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 $N_s=2.2\mathrm{}\times {10}^{12}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$ for $n$-type material and 5×${10}^{12}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{eV}}^{-1\mathrm{}}$ for $p$-type material; flat-band condition is satisfied when $E_F$ is 0.2 eV above midgap.