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) investigation of indium surface segregation for As-stabilized Ga1-xInxAs and Al1-xInxAs ternary bulk alloys grown by molecular beam epitaxy on InP(001) substrates in the following conditions: (i) lattice-matched Ga0.47In0.53As and Al0.48In0.52As grown at 300 and 525 degrees C, and (ii) compressive strained and relaxed Ga0.25In0.75As grown at 525 degrees C. Our results show, first, that a chemically shifted component indicative of an InAs surface layer appears within the In 4d core level spectrum, 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 direct effect on the indium surface segregation at least for Ga0.25In0.75As at 525 degrees C. We analyse and interprete the indium segregation phenomenon as induced by differences in In, Al and Ga surface mobilities during the layer by layer epitaxial growth process.