GAP, GAAS, AND INP NITRIDATION AT ROOM-TEMPERATURE BY N2 ADSORPTION ON (110) SURFACES MODIFIED BY ALKALI-METALS

The effect of molecular nitrogen exposures on the (110) surfaces of GaP, GaAs and InP modified by alkali metal overlayers was investigated by core level spectroscopy using synchrotron radiation. In the presence of alkali metals, these surfaces exhibit nitrogen uptake and nitride formation at room temperature, while the clean surfaces remain unaffected by N2 exposures. The nitridation products consist mainly of InPNx on InP, while formation of mixed nitrides on both anion and cation sites like GaN, GaN1+y and GaAs1-xNx occurs for GaAs (with much higher nitridation states than in the case of direct plasma nitridation). The situation for GaP is found to be intermediate. In contrast to the only other studied case of promoted semiconductor nitridation - the Na or K/Si(100) system, a reaction between the adsorbate and the surface is found to be a prerequisite in the case of III-V semiconductors, since nonreactive interfaces do not exhibit nitridation. This suggests that surface defects play a central role in alkali-metal promoted nitridation of III-V semiconductors.