Multiple quantum-well GaAs/Ga0.8Al0.2As structures which were uniformly Si-doped, to concentrations ranging from 1017 to 1019/cm3, were grown by means of molecular-beam epitaxy in order to study the effects of the background Si dopant level upon the Zn diffusion-induced disordering. After Zn diffusion (575C, 4 or 16h), cleaved wedges of the samples were investigated by means of secondary-ion mass spectrometry and transmission electron microscopy. The results showed that completely and partially disordered regions were always behind the Zn diffusion front. A dependence of the effective Zn diffusivity and of the disordering rate of the structure upon the background Si dopant level was observed. The effective Zn diffusivity and the disordering rate significantly decreased with increasing background Si concentration. Before Zn diffusion, the photoluminescence spectra of Si-doped structures exhibited an increase in intensity of the Si donor column-III vacancy complex emission band with increasing Si dopant level. This indicated that the concentration of column-III vacancies in the structures increased as the background Si concentration was increased. After Zn diffusion, a large decrease in intensity of the column-III vacancy-related emission band was observed in the photoluminescence spectra from Zn-diffused regions. A model that was based upon the so-called kick-out mechanism of Zn diffusion was proposed in order to explain the effect of the background Si doping level upon the effective Zn diffusivity. The model showed that the effective Zn diffusivity was controlled by the concentration of column-III interstitials behind the Zn diffusion front, and by the donor concentration in the sample. Column-III interstitials were generated during the incorporation of Zn into the crystal lattice. The supersaturation of these interstitials behind the Zn diffusion front was responsible for the enhancement of Al-Ga interdiffusion. Because column-III interstitials and column-III vacancies could mutually annihilate, the concentration of column-III interstitial and column-III vacancies in Zn-diffused regions decreased with increasing Si doping level; thus leading to a retardation of Zn diffusion into the structure. A decrease in effective Zn diffusivity, caused by an increase in the donor concentration of the samples, was also demonstrated. The results revealed effects of the Fermi level and of interactions between point defects during the Zn diffusion-induced disordering of GaAs/AlGaAs multi-layered structures.

N.H.Ky, J.D.Ganière, F.K.Reinhart, B.Blanchard: Journal of Applied Physics, 1996, 79[8], 4009-16