NON-EQUIVALENCE OF DIRECT AND REVERSE INTERFACES IN ALAS-GAAS SUPERLATTICE STRUCTURES AS EVIDENCED BY X-RAY-DIFFRACTION

In this paper we study the relation between interface roughness and X- ray intensity diffracted by a short period n1(AlAs)-n2(GaAs)/GaAs(001) superlattice (SPSL). A theoretical approach shows that introducing th e same graded composition profile on both sides of the GaAs well equal ly reduces the intensity of all high order satellites. However, if the profile is not the same at both interfaces, the intensity variation o f the satellites is completely different, depending on their order. We show that the extinction rule of satellites is no longer valid and th erefore constitutes a very sensitive criterion of the non-equivalence of the direct and reverse interfaces. As an example, we apply this cri terion to refine the structure of 8(A]As)-20(GaAs) SPSL. The best agre ement between observed and calculated SL structure factors is obtained for an asymmetric-shape GaAs well. The interface widths are 6 and 4 m onolayers, and the best-fit model gives an R factor of 0.028.