The dislocation density of a GaAs layer grown on a vicinal (001) Si substrate has been studied as a function of Si miscut angle by X-ray diffraction technique. The high-resolution X-ray diffractometer equipped with Bartels monochromator in double and triple crystal modes was used.
Using the kinematical theory of X-ray scattering by a crystal with dislocations developed by Hordon and Averbach [1], the dislocation content was investigated by analysing the diffraction peak profiles, the reciprocal lattice maps and the Williamson-Hall plots for selected peaks.
The results were described by a model assuming that, as a result of the 3-D layer growth and GaAs cell deformation character (caused by difference of thermal expansion coefficient), subgrains have dislocations inside and at the boundaries. In this case, dislocations at the subgrain boundaries and surrounding strain cause the planes tilt effect. The broadening of diffracted peaks caused by strain inside subgraines and by tilt from dislocations at the boundaries is independent of each other [2]. This model explains the decrease of dislocation density in the layer after high pressure-high temperature treatment.
Our results show that the increase of substrate miscut angle causes a decrease of mismatch strain and dislocation density. The data obtained from X-ray measurements and other experimental methods are compared.

1. M.J.Hordon, B.L.Averbach. (1961) Acta Metallurgica v.9, 273-246
2. C.Ferrari et al. (1996) Applied Physics Letters. 69 (27), 4233-4235