Implication of hydrogen-induced boron passivation in wet-chemically cleaned Si(111):H

Abstract Atomically-flat, hydrogen-terminated Si(111) surfaces with a boron concentration range of 4.5 ∼ 11 × 10 18 cm −3 have been prepared by a standard RCA cleaning step and subsequent 40% NH 4 F immersion followed by pure water dipping. The surface Fermi level for as-prepared Si(111) lies near midgap as confirmed by X-ray or ultraviolet excited photoelectron spectroscopy (XPS/UPS) and Kelvin probe measurements although occupied gap states density as low as 10 11 cm −2 at most is verified from an extremely low photoelectron yield for photons with energies below ∼ 5 eV. Annealing at 360°C for 5 min causes the Fermi level to shift towards the valence-band maximum top by ∼0.2 eV without an appreciable increase in the gap state density and a change in hydrogen surface termination. These observations imply a hydrogen-induced passivation of boron atoms in a surface layer during wet-chemical cleaning and the reactivation of such passivated boron atoms by 360°C annealing. For annealing temperatures above 460°C, hydrogen desorption from the surface results in a true pinning of the Fermi level close to midgap because of the generation of surface gap states.