Identical GaAs/Al0.2Ga0.8As multiple-quantum-well (MQW) structures uniformly doped with Si at various concentrations ranging from 1x10(17) to 1X10(19) cm(-3) are grown by molecular-beam epitaxy to study the effects of the background Si-doping level on the Zn diffusion-induced disordering process. After Zn diffusions at 575 degrees C for 4 and 16 h, the structures are investigated by secondary-ion-mass spectrometry, and by transmission electron microscopy on cleaved wedges of the sample. The results show that the totally and partially disordered regions are always behind the Zn diffusion front. A dependence of the effective Zn diffusivity and of the disordering rate of the structures on the background Si-doping level is observed. The effective Zn diffusivity and the disordering rate are significantly reduced with increasing background Si concentration. Before Zn diffusion, photoluminescence spectra of the Si-doped MQW structures exhibit an increase in intensity of the Si donor-column-III vacancy complex emission band with increasing Si-doping level. This indicates that the concentration of column-III vacancies in the MQW structures increases as the background Si concentration increases. After Zn diffusion, an important decrease in intensity of the column-III vacancy related emission band is observed on the photoluminescence spectra taken in the Zn-diffused regions. The systematical analysis of the photoluminescence spectra of the Zn-diffused MQW structures as a function of diffusion time and as a function of etching depth below the sample surface makes it possible to describe the physical processes occurring during Zn diffusion. A model based on the ''kick-out'' mechanism of Zn diffusion is proposed to explain the effect of the background Si-doping level on the effective Zn diffusivity. The model shows that the effective Zn diffusivity is controlled by the concentration of column-III interstitials behind the Zn diffusion front and by the donor concentration in the sample. During the incorporation of Zn into the crystal lattice, column-III interstitials are generated. The supersaturation of these interstitials behind the Zn diffusion front is responsible for the enhancement of Al-Ga interdiffusion. Since column-III interstitials and column-III vacancies can mutually annihilate, the concentration of column-III interstitial and column-III vacancy in the Zn-diffused region is reduced with increasing Si-doping level, leading to a retardation of Zn diffusion into the MQW structure. On the other hand, a decrease of the effective Zn diffusivity caused by an increase in donor concentration in the samples is also demonstrated. Our results give evidence for the Fermi-level effect and the interactions between different point defects during Zn diffusion-induced disordering of GaAs/AlGaAs multilayered structures. (C) 1996 American Institute of Physics.