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X ray techniques have enabled a fast characterisation of a new VG Semicon V90S MBE system for growth of Si and SiGe material. X-ray rocking curves have allowed characterization of SiGe layers to tolerances as tight as ± 0.1 At%. X-Y uniformity measurements demonstrated that layers are grown to + 0.5 % over a 150 mm wafer. Information on the flux rate uniformity during growth can be obtained from analysis of superlattice structures. These enable calculation of "worst case" flux variation during a growth run. An empirical relationship has been found that enables the prediction of the degree of residual strain remaining in a buffer structure grown beyond the metastable critical thickness.