SEXAFS STUDY OF THE GAAS INP INTERFACE

Extended X-Ray Absorption Fine Structure measurements have been perfor med at the Ga and As K-edge of a nominal 3 ML GaAs grown by Molecular Beam Epitaxy on a InP(100) substrate deoxidized in As atmosphere. We e xploited the in-plane linear polarization of the synchrotron radiation measuring SEXAFS spectra taken with the polarization vector parallel and perpendicular to the growth direction. By comparing the ratio of t he coordination numbers of the pairs As-Ga As-In. Ga-As, taken at the two different angles of the polarization vector, a quantitative model of the interface is obtained. Two well defined layers form on the InP substrate giving rise to the following sample structure: 3 ML GaAs/3 M t. InAs/lnP. This rules our the formation of InGaAs or InGaAsP layers at the interface.