COMMENSURATE AND INCOMMENSURATE PHASES AT RECONSTRUCTED (IN,GA)AS(001) SURFACES - X-RAY-DIFFRACTION EVIDENCE FOR A COMPOSITION LOCK-IN

Surface chemical ordering of group III elements in the ternary alloy I nxGa1-xAs, stabilizing the 2 X 3 reconstruction at the surface composi tion In0.67Ga0.33As, is demonstrated on the basis of x-ray diffraction data. An incommensurate 2 X n reconstruction is observed for lower In surface concentrations, achieved by burying an InAs monolayer under a number of GaAs layers and letting the In surface segregation process operate. A quantitative account of the intensity measured in the incom mensurate phase is obtained by using a probabilistic distribution of G a- and In-rich structural elements.