NOVEL DISLOCATION-STRUCTURE AND SURFACE-MORPHOLOGY EFFECTS IN RELAXEDGE SI-GE(GRADED)/SI STRUCTURES/

The defect structure in relaxed graded Ge/GexSi1-x/Si structures grown on (001) exact and (001) off-cut substrates using ultra-high vacuum c hemical vapor deposition was characterized using transmission electron microscopy (TEM), atomic force microscopy, and electron beam induced current. The samples grown on off-cut (001) substrates showed a remark able improvement in surface roughness and dislocation pile-up densitie s. By applying both a dislocation blocking criterion and surface rough ness to graded Si-Ge/Si(001) structures, we can predict the formation of dislocation pile-ups in graded structures. Nonparallel misfit dislo cation networks in off-cut wafer samples are not as efficient al block ing perpendicular dislocation motion, leading to a large reduction in dislocation pile-up density. The Lower pile-up density on layers grown on off-cut wafers results in less stress-induced surface instability during growth, leading to surfaces with much lower roughness. TEM stud ies revealed that the array of 60 degrees dislocations, that usually f orms to relieve the misfit stress, transforms into a lower energy hexa gonal dislocation network consisting of edge dislocations with Burgers vectors of the type 1/2[110], 1/2[<(1) over bar>10], and [100]. Such reactions were found to be more prevalent in tile samples grown on off -cut substrates. Favorable intersections of {111} type planes on the o ff-cut substrates were found to aid such reactions. (C) 1997 American Institute of Physics.