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 ESF and bulk Fermi level EF. The films were prepared by rf plasma decomposition of SiH₄ doped with 0-2 vol% B₂{H}₆$ or 0-2 vol% P${H}₃$. ${E}SF$ 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 ${N}ₛ=10×{}{10}¹²$ ${cm}^{{-}2}eV^-1 for n-type material and 13×{}10¹² cm^-2{eV}^{{-}1}$ for $p$-type material; the bands are flat (${E}F={E}SF$) when ${E}F$ is 0.1 eV above midgap. In the case of oxidized surfaces ${N}ₛ=2.2×{}{10}¹²$ ${cm}^{{-}2}eV^-1 for n-type material and 5×{}10¹² cm^-2{eV}^{{-}1}$ for $p$-type material; flat-band condition is satisfied when ${E}F$ is 0.2 eV above midgap.