ARSENIC PASSIVATION OF MBE GROWN GAAS(100) - STRUCTURAL AND ELECTRONIC-PROPERTIES OF THE DECAPPED SURFACES

The passivation properties and thermal stability of As on GaAs(100) were studied under ultra-high vacuum (UHV) conditions for As caps of different thicknesses and storage times in air. The As desorption was monitored by mass spectrometry (QMS) and the substrate surface quality by means of Auger electron spectroscopy (AES), electron diffraction (LEED) and Raman spectroscopy (RS). Additional desorption experiments were performed in an oven in N2 atmosphere. These samples were then investigated by spatially resolved Raman spectroscopy under atmospheric conditions. The Raman spectra of the air exposed samples show that the cap consists of an amorphous As layer with small As2O3 crystallites on top. AES investigations reveal in addition strong carbon contaminations. Arsenic desorption in UHV takes place in two steps, a first one at around 160-degrees-C which can be attributed to the desorption of the As2O3 Crystallites and a second one at around 350-degrees-C due to the desorption of the amorphous As layer. From 360-degrees-C on with further increasing temperature (1 X 1), (2 X 4) and (4 X 1) reconstructions are observed by LEED. The band bendings at the surfaces as determined by Raman scattering were found to be not systematically related to the differently reconstructed surfaces. Residual carbon contaminations were found after Arsenic desorption in many cases, whereas the surfaces are always free of oxygen contaminations.