We measured the energy and density of near-surface defects in hydrogenated amorphous silicon, germanium, and their alloys by total-yield photoemission spectroscopy. The defects lie 0.56 eV above the valence-band edge, independent of alloy composition. The defect density at the clean surface is constant at ∼2×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. These values agree exactly with the equilibrium theory of dangling bonds, so that our experiments furnish the first evidence for thermal equilibration of semiconductor surface defects.

• Received 19 March 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.629