INVESTIGATION OF SE CAPPING OF EPITAXIAL GA2SE3 LAYERS

Epitaxial layers of vacancy-ordered Ga2Se3 were grown onto GaAs(100) s ubstrates using a heterovalent V-VI exchange reaction. For this purpos e the substrates were annealed to 860 K in a H2Se flow. Capping was ac hieved 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 surfa ces as well as the thermal stability of the caps were investigated usi ng Raman, Auger and photoelectron spectroscopy after annealing steps o f 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 crysta l quality and extremely low contamination levels. This allows clean Ga 2Se3 surfaces to be investigated using angle resolved valence band and core level photoemission. The corresponding results are compared to t hose obtained for in situ Se treated GaAs in order to identify the che mical reactions at such surfaces.