Morphology and chemistry of S-treated GaAs(001) surfaces

The morphology and chemistry of S-treated GaAs(001) surfaces have been investigated by using an atomic force microscope (AFM) and a synchrotron radiation scanning photoemission microscope (SPEM) for a sample (A) which was directly blown dry with N-2 after the S-treatment and for another sample (B) which was rinsed by DI water and finally blown dry with N-2 after the S-treatment. AFM and SPEM images show for sample A a very inhomogeneous surface morphology, while the surface morphology of sample B appeared to be very homogeneous. On the surface of sample A, an inhomogeneous distribution of particles was observed by AFM. Nearly all these particles could be removed by the water rinse. Laterally resolved core level spectra analysis shows that on both samples the S bonds mainly to Ga. Only traces of As-S and As-As bonds exist at the sample surface while no S-S bonds could be detected. From the analysis of the O 1s core level it can be deduced that only a small GaAs surface fraction is oxidized. Furthermore, O-S bonds are present at the surface. On the sample before the water rinse, the number of O-S bonds is laterally inhomogeneously distributed. The number of O-S bonds can be drastically reduced by the water rinse, which also results in a homogeneous distribution of those bonds. We deduce that the O-S bonds belong to sulfate SOinfinity deposits at the sample surface which are the particles that were imaged by AFM.