COMPARISON OF DIFFERENT SI GE ALLOY BUFFER CONCEPTS FOR (SIMGEN)(P) SUPERLATTICES/

Fully relaxed buffers of final Ge concentration x(f) are needed to gro w strain-symmetrized superlattices. Different concepts of such a buffe r of step graded, linear and quadratic concentration profiles x = x(z) from x = 0 to x(1000 nm) = x(f) as well as subsequent 500 nm of homog eneous Si1-xGex alloy of x = x(f) were performed. These buffers are in vestigated for a minimum dislocation density determined by X-ray diffr action and by etching. We will show that a parabolic concentration pro file, starting with a positive gradient dx/dz(z = 0) > 0 and turning t o 0 for constant alloy x = x(f) at a thickness of z = 1000 nm, gives t he best buffer concept.