Due to electron diffraction in the atomic network, the measurement of core electron peak intensity or Auger electron peak intensity from a single crystal surface as a function of the electron take-off angle gives rise to plots in which pronounced fine structure is superimposed on the instrumental response function.Of course, in amorphous samples or polycrystals, where the arrangements of atoms are macroscopically randomized, such fine structures are averaged. In these cases, the angular distribution curves (ADCs) show smoothly-varying curves containing no marked structure. Perfectly crystalline surfaces provide the other extreme situation giving ADCs with maximum anisotropy. So we can draw some qualitative conclusions from the measurement of the anisotropy degree of the XPD patterns, which is directly related to the change of surface structure and stoichiometry.Using the XPD method, we examine the stoichiometry variations and the damage induced by different technological processes including (i) the case of the acidic etching of GaAs (001) surfaces (ii) the reactive ion etching of InP (001) substrates and the subsequent epitaxial growth of InP layer on this etched surface.