We report successful growth of the n-type strained GaInAsP/InP multiple quantum well (MQW) structures using all solid source molecular beam epitaxy and the effects of doping density in the wells on the quality of the MQW structures. In the high-resolution X-ray diffraction curves, well-defined sharp satellite peaks up to the 15th order can be observed, indicating a very high crystalline quality of the MQW structures. With increase of Si-doping concentration in the wells, the lattice mismatch increases. The FWHM of the zero-order peak also increases and fits a logistic function well with the doping density. The period of the MQW structures is found to decrease and the intensity of the first-order satellite peak to decays exponentially. All the observations can be explained by the changes in lattice constant, interface defects, dopant diffusion and possibly growth rate, caused by high doping in the wells of the MQW structures. (C) 2002 Elsevier Science B.V. All rights reserved.