IMPLICATION OF HYDROGEN-INDUCED BORON PASSIVATION IN WET-CHEMICALLY CLEANED SI(111)H

Atomically-flat, hydrogen-terminated Si(111) surfaces with a boron con centration range of 4.5 similar to 11 x 10(18) cm(-3) have been prepar ed by a standard RCA cleaning step and subsequent 40% NH4F immersion f ollowed 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 al though occupied gap states density as low as 10(11) cm(-2) at 5 min ca uses the Fermi level to shift towards the valence-band maximum top by similar to 0.2 eV without an appreciable increase in the gap state den sity 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 at 360 degrees C annealing. For annealing temperatures abo ve 460 degrees C, hydrogen desorption from the surface results in a tr ue pinning of the Fermi level close to midgap because of the generatio n of surface gap states.