Dislocations in compositionally graded virtual substrates and InAsSb epitaxial layers for long wavelength (8-12 mu m) photodetectors have been investigated with high-resolution x-ray topography (XRT). By varying the imaging conditions, the properties of the virtual substrate and InAsSb could be individually characterized. We observe the formation of misfit dislocations near the interface predominantly along the (110) direction and with less relaxation along the (1-10) direction. The misfit dislocations do not form a uniform array of dislocations but rather appear as dislocation bundles. Threading dislocation clusters, which could limit device performance, are observed along the misfit arrays with a density SIM;1 x 10(5) cm(-2) and a total averaged density of less than 1 x 10(6) cm(-2). The prospects for using XRT for further optimization of virtual substrate and development of low defect bulk InAsSb layers are discussed. Published by AIP Publishing.
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