HYDROGEN ACTION IN THE SURFACE SPACE-CHARGE REGION OF HIGHLY DOPED SILICON

The action of atomic hydrogen on clean cleaved (111) surfaces of highly doped silicon samples, both phosphorus ([n] = 2 x 10(19) cm-3) and boron ([p] = 4 x 10(19) cm-3) doped has been compared to the case of lightly doped samples ([n] = 1 x 10(14) cm-3). Once cleaved under ultra high vacuum, the samples were exposed to increasing doses of atomic hydrogen up to saturation. Before and after each hydrogen exposure exposure, the Si (111) 2 x 1 surface was studied by low energy electron diffraction (LEED) and photoemission yield spectroscopy (PYS). The compared PYS measurements show that H atoms adsorbed on the Si (111) surface at room temperature do totally compensate the shallow-acceptor impurities (boron) and only partially the shallow-donor impurities (phosphorus) in the space charge region. They also remove the surface dangling bond states. These effects are reversible upon heating under vacuum. Both surface stresses and space charge electric field play a role in this compensation effect.