RELAXED SI0.7GE0.3 BUFFER LAYERS FOR HIGH-MOBILITY DEVICES

The minimum epitaxial layer thickness required to produce relaxed, the rmally stable, Si0.7Ge0.3 buffer layer structures for high electron- a nd hole-mobility devices has been determined, using high resolution x- ray diffraction. A 1.4-mu m-thick layer, step graded to x=0.35, is suf ficiently thick so that the residual strain in a uniform composition S i0.33Ge0.67 layer grown on top of it is essentially independent of thi ckness or growth temperature of the layer. Such structures are stable when annealed at 750 degrees C. (C) 1995 American Institute of Physics .