FABRICATION OF RELAXED GESI BUFFER LAYERS ON SI(100) WITH LOW THREADING DISLOCATION DENSITY

We describe the fabrication of relaxed GeSi buffer layers on Si(100) with low threading dislocation densities. The samples were grown by molecular beam epitaxy at high substrate temperatures (900-degrees-C for low Ge content). The basic building block is composed of a compositionally graded GexSi1-x strain relief layer on Si(100) substrates, followed by a cap layer with uniform composition. The degree of relaxation is studied by a combination of Rutherford backscattering and X-ray diffraction, while the dislocation density is determined by transmission electron microscopy and electron beam induced current. Photoluminescence is used to probe the electronic quality. We show that the samples studied are nearly 100% relaxed (within the experimental certainty), with typical threading dislocation density in the low 10(6) cm-2 (approximately two orders of magnitude lower than that in GeSi layers not compositionally graded and with the same final Ge content). The sharp band-edge related photoluminescence peak proves the high electronic quality of the GeSi cap layers, and the luminescence peak energy supports the near 100% relaxation as observed by X-ray.