X-ray standing wave measurements on III–V compound heterostructures

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New applications of the x-ray standing wave method are described, in which not only Bragg reflections from the substrate, but also from a heteroepitaxial layer and from a superlattice satellite are utilized. The investigated samples are an InP/InGaAsP structure on InP(001) and a short-period AlAs/GaAs superlattice on GaAs(001). For efficient detection of the photoelectron yield without vacuum requirements, the sample was placed inside a gas cell, and the induced photocurrent was monitored. In addition to the electron yield, which probes only a thin surface layer, the depth-integrating x-ray fluorescence was analyzed. The results give new insights into the structure of heteroepitaxial systems and their buried interfaces, as well as information about electron escape depths and spatial coherence of x-ray wavefields.