Surface chemistry of InAlAs after (NH4)2Sxsulphidation

The (NH 4 ) 2 S x sulphidation of MBE-grown InAlAs layers was studied in order to passivate GaInAs/InAlAs/InP HEMT microelectronic devices. The chemical composition of sulphurized InAlAs (100) surfaces was investigated by x-ray photoelectron spectroscopy (XPS). The S-treated surfaces were compared with an oxidized chemically etched InAlAs surface (after removing the top GaInAs capping layer) and with an 'as-grown' InAlAs surface. It was observed that the InAlAs layers could be completely deoxidized and that, depending on the experimental conditions, a thin (2 monolayers (ML)) or a thick (8 ML) sulphide layer could be prepared. XPS analysis of the sulphide-tested surfaces indicated that oxidation was strongly suppressed but that the segregation of elemental As was not effectively suppressed. In the case of thick sulphide layers, strong chemical passivation occurs, since no degradation of the surface chemistry was observed after one month's exposure to air.