Stoichiometry and discommensuration on InxGa1-xAs/GaAs(001) reconstructed surfaces: A quantitative x-ray diffuse-scattering study

A quantitative estimate of the In/Ga surface concentration ratio in ultrath in (In, Ga)As strained layers, grown by molecular-beam epitaxy on a GaAs(00 1) substrate, is obtained using grazing incidence x-ray diffraction and dif fuse-scattering measurements. The commensurate 2x3 reconstruction is interp reted as due to cation ordering in the surface unit cell, locking the surfa ce composition at the value In2/3Ga1/3As. Incommensurate 2xn reconstruction s with n<3 (n>3) are described in terms of indium-depleted (-enriched) surf ace layers characterized by a statistical distribution of faults in the ide al 2 x 3 atomic arrangement. Within a defined temperature range 450-490 deg rees C, a unique correspondence between the incommensurability parameter n and the indium surface fraction is established on the basis of a formulatio n of the diffuse scattering distribution. [S0163-1829(98)04648-7].