HREELS INVESTIGATION OF HYDROGENATED GAAS(110) SURFACES

The interaction of atomic hydrogen with the cleaved GaAs (110) surface has been investigated by high-resolution electron energy loss spectro scopy (HREELs), at primary energies of 5 and 15 eV. analysing the loss es associated with three different mechanisms: (i) low-energy surface collective excitations (surface TO phonon and dopant-derived free-carr ier plasmon); (ii) the stretching of the Ga-H and As-H bonds; and (iii ) the electronic losses above the fundamental gap, involving both surf ace and bulk electronic states. The first kind of loss is very sensiti ve to H exposure and shows that hydrogen induces a band bending at the lowest exposures. The vibrational part of the spectrum indicates that the exposure of 10(4) L corresponds to a coverage of one monolayer an d that H binds to both Ga and As over the whole coverage range. The re gion of the electronic transitions indicates the disappearance of tran sitions of the clean surface and the appearance of new transitions cha racteristic of the H covered surface. At high exposures the growth of a very strong background is consistent with the presence of small meta llic Ga clusters. This result is also consistent with the modification s, at the same exposures, of the low-energy region of the spectrum.