We investigate the effects of Si doping on the strain relaxation of the compositionally step-graded (Al)GaInP buffers grown by metal-organic chemical vapor deposition on (0 0 1) GaAs substrates with different miscuts toward (1 1 1)A. It is found that in the 2 degrees samples, high Si doping can reduce both the alpha and beta dislocation densities by delaying and suppressing the formation of phase separation in the buffer. In contrast, in the 7 degrees samples, Si dopants deteriorate the buffer quality through increasing the dislocation density accompanying with the tilt reduction along the [1 1 0] direction, and a striking feature, bunches of beta dislocations away from the interfaces, is observed in the [1 1 0] cross-sectional transmission electron microscopy images. A cross-slip mechanism closely associated with the pinning effect of Si on alpha dislocation motion is proposed to explain the multiplication of beta dislocations. These results indicate that selecting a moderate Si doping density and substrate miscut are critical for the design and fabrication of metamorphic optoelectronic devices. (C) 2013 Elsevier B.V. All rights reserved.