INVESTIGATION OF SE CAPPING OF EPITAXIAL GA2SE3 LAYERS

Epitaxial layers of vacancy-ordered Ga2Se3 were grown onto GaAs(100) substrates using a heterovalent V-VI exchange reaction. For this purpose the substrates were annealed to 860 K in a H2Se flow. Capping was achieved by cooling the samples under continued gas flow. After storage in air for several weeks the morphology of the samples was studied by scanning electron and optical microscopy. The composition of the surfaces as well as the thermal stability of the caps were investigated using Raman, Auger and photoelectron spectroscopy after annealing steps of 15 min up to 650 K in UHV. The cap is found to consist of amorphous Se after deposition onto the Ga2Se3 surface. The Se crystallises upon annealing to 440 K. Increasing the temperature leads to the desorption of the Se overlayer, a process which is completed at about 570 K. The Ga2Se3 surfaces obtained are morphologically smooth, show good crystal quality and extremely low contamination levels. This allows clean Ga2Se3 surfaces to be investigated using angle resolved valence band and core level photoemission. The corresponding results are compared to those obtained for in situ Se treated GaAs in order to identify the chemical reactions at such surfaces.