UNIQUE X-RAY-DIFFRACTION PATTERN AT GRAZING-INCIDENCE FROM MISFIT DISLOCATIONS IN SIGE THIN-FILMS

Grazing-incidence x-ray diffraction (GIXD) permits the direct measurem ent of in-plane lattice parameters of SiGe films that are too thin to yield good results from normal-geometry triple-axis techniques. A uniq ue ''X''-shaped pattern has been seen in H-K reciprocal space maps of diffracted x-ray intensity from SiGe films that have relaxed via a mod ified Frank-Read mechanism. Contours of intensity are seen along the [ 110] directions from the ((4) over bar 00) reciprocal lattice peak wit h the introduction of the first dislocations. For higher dislocation d ensities the X-shaped contours are anisotropically distorted and a sat ellite peak, corresponding to the lattice parameter for a partially re laxed film, becomes identifiable at lower H. In contrast, H-K reciproc al-space contours from thin SiGe films that have relaxed by roughening and subsequent random nucleation of dislocations display broad, oval- shaped contours centered at the ((4) over bar 00) reciprocal lattice p oint for the film. Numeric simulations of GIXD from a variety of dislo cation arrangements were performed in order to understand the origin o f the X pattern. We show that this pattern arises from an array of lon g misfit dislocations running in the [110] directions. The anisotropic distortion of the X pattern arises at higher dislocation densities fr om orthogonal intersections of dislocations with equal Burgers vector, which are characteristic of dislocation networks generated by the mod ified Frank-Read mechanism. We also verify that the measured values of the in-plane lattice parameter, together with the out-of-plane lattic e parameter determined from the symmetric (004) reflection, lead to ac curate calculation of the composition and strain in these SiGe layers. (C) 1996 American Institute of Physics.