IMPORTANCE OF DEFECTS AND DOPANT NATURE IN ALKALI-METAL III-V-SEMICONDUCTOR INTERFACE FORMATION AND PROMOTED OXIDATION

The room-temperature oxidation of p- and n-type GaSb(110) surfaces modified by a sodium or a rubidium overlayer is investigated by means of core-level and valence-band photoemission spectroscopy using synchrotron radiation. The oxidation rate of the GaSb(110) is increased by nearly 6 orders of magnitude in the presence of the alkali-metal adsorbate. This results in the formation of mixed Ga2O3 and Sb2O5 oxides. A complete oxidation of the GaSb(110) surface only occurs when a strong reaction between the alkali overlayer and the substrate takes place, which indicates that defects play a central role in the reaction similarly to the previously observed case of alkali-metal-promoted nitridation of other III-V semiconductor surfaces. This behavior is very different from the one observed in the case of alkali-metal-promoted oxidation or nitridation of elemental semiconductors such as silicon where no reaction between the adsorbate and the substrate occurs. Interestingly, the p-type (Zn doped) surfaces were, in general, found to be more reactive than the n-type (Te doped) ones, which suggests that the nature of the dopant might also play some role in the formation of reactive interfaces. The results indicate that surface defects seem to play an important role in alkali-metal-promoted reactions of III-V compound semiconductors.