On the origin of the positive charge on hydrogenated Si surfaces and its dependence on the surface morphology

Chemically and electrochemically hydrogenated Si surfaces are investigated by surface photovoltage technique, scanning tunneling microscopy, and Fourier transform infrared spectroscopy. The surface states are predominantly of the donor type which can act as fixed positive surface charge (Q(f)) as well as fast surface states depending on the surface morphology and the applied field voltage. The donor type surface states on hydrogenated Si surfaces can be related to water molecules adsorbed at surface imperfections. The lowest values of Q(f) and of the density of surface states in the minimum D-it(min) (10(10) cm(-2) and 10(10) eV(-1) cm(-2), respectively) are reached on macroscopically rough hydrogenated surfaces which are locally very smooth. (C) 1999 Elsevier Science B.V. All rights reserved.