IN-SITU XPS INVESTIGATION OF INDIUM SURFACE SEGREGATION FOR GA1-XINXAS AND AL1-XINXAS ALLOYS GROWN BY MBE ON INP(001)

We present an in situ X-Ray photoemission spectroscopy (XPS) investiga tion of indium surface segregation for As-stabilized Ga1-xInxAs and Al 1-xInxAs ternary bulk alloys grown by molecular beam epitaxy on InP(00 1) substrates in the following conditions: (i) lattice-matched Ga0.47I n0.53As and Al0.48In0.52As grown at 300 and 525 degrees C, and (ii) co mpressive strained and relaxed Ga0.25In0.75As grown at 525 degrees C. Our results show, first, that a chemically shifted component indicativ e of an InAs surface layer appears within the In 4d core level spectru m, Second, below this InAs top layer, we found a composition gradient which increases with growth temperature and is greater for AlInAs than for GaInAs compounds. Finally, we show that strain seems to have no d irect effect on the indium surface segregation at least for Ga0.25In0. 75As at 525 degrees C. We analyse and interprete the indium segregatio n phenomenon as induced by differences in In, Al and Ga surface mobili ties during the layer by layer epitaxial growth process.