EVOLUTION OF STRAIN RELAXATION IN STEP-GRADED SIGE/SI STRUCTURES

Strain relaxation in a series of step-graded SiGe/Si structures has been quantitatively investigated by high-resolution x-ray diffraction measurements. We show that beyond a critical thickness, dislocations nucleate continuously as layers with higher Ge mole fraction are added to the structure and that the mismatch strain at which nucleation occurs is therefore essentially constant. It had been found empirically that a lower growth temperature is required to suppress roughening of layers with higher Ge mole fraction, even in graded structures. We prove that this is not because the strain increases, but rather because of the lower melting temperature of layers with higher Ge content.© 1995 American Institute of Physics.