The absolute lattice parameters of single‐ and polycrystalline materials have been measured to within a few parts per million with a high‐resolution diffractometer. The problems associated with 'zero errors' and sample centring on the goniometer are eliminated and high precision is achieved by virtue of the exceedingly high angular resolution of the instrument. The high‐resolution multiple‐crystal multiple‐reflection diffractometer is used to determine the lattice parameter with a single quick measurement on a range of 'perfect' semiconductor‐substrate materials, layer structures and inhomogeneous samples. The various corrections and alignment procedures associated with this method are discussed.

We have studied the profiles of the Bragg peaks and diffuse scattering in reciprocal space along both the plane perpendicular (qperpendicular to ) and plane parallel (q/sub ///) directions for sample structures consisting of layers of In0.1Ga0.9As grown by molecular beam epitaxy on (001) oriented GaAs substrates. The samples have different layer thicknesses and different dislocation distributions. We have measured the dislocation distributions in the interfaces using plan view transmission electron microscopy. We find that, for thin layers with low dislocation densities, the diffraction profiles in both the plane perpendicular (qperpendicular to ) and plane parallel (q/sub ///) can be modelled by considering two components of the diffraction profile, namely, dynamical scattering from the coherently coupled regions of perfect layer between dislocations and diffuse scattering from decoupled regions around the dislocations. From the q/sub /// profile a lateral dimension can be associated with the regions that give rise to the diffuse scattering, and we show that this dimension scales with the layer thickness. For thicker layers with higher dislocation densities, the strain fields of the dislocations overlap. In this case the diffraction profiles in (qperpendicular to ) are modelled by considering the ratio of the depth of coherently scattering decoupled crystal, above the dislocation array, with the total depth of the layer, assuming that scattering from the greatly distorted crystal close to the array is lost. Along q/sub /// the diffuse scattering is discussed on the basis of a statistical distribution of finite correlation lengths and microscopic tilts.

The elucidation of the structure of semiconductor multilayers can be adequately determined by X-ray methods but the interpretation is not always straightforward. In this paper we introduce the idea of full three-dimensional diffraction-space mapping to obtain information on the three-dimensional structure of imperfect materials. We also stress the importance of this method for the interpretation of the data from high-resolution X-ray diffractometry. The presence of defects and diffraction effects can create significant changes to the diffraction pattern that require a more complete analysis than that obtained from simple profiles. These subtle influences can in general only be understood by diffraction-space mapping. Interpretation of diffraction-space maps from the high-resolution multiple-crystal multiple-reflection diffractometer permits the use of three extra very powerful tools. The first is multiple-crystal topography so that the diffraction-space intensity features can be related to lateral contrast on the photographic emulsion, the second is the accurate determination of lattice parameters and the third is the simulation of the diffraction shapes using dynamical theory.

This paper illustrates the procedure for extracting structural information available from x-ray diffraction space mapping and topography. The methods of measuring, the residual strain, macroscopic tilts, microscopic tilts and their lateral dimensions, and the strain field disruption emanating from the interfacial defects are presented. Partially relaxed thick InGaAs layers on GaAs substrates were studied and it was concluded that the relaxation and macroscopic tilting were anisotropic, the microscopic tilting reduced with thickness, and the interfacial disruption did not continue to increase with increasing relaxation. A ‘‘mosaic grain growth’’ model is postulated to account for the diminishing microscopic tilt spread and increasing topographic contrast with layer thickness.

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