Background doping effects on Zn diffusion in GaAs/AlGaAs multiple-quantum-well structures

The effects of background n- and p-type doping on Zn diffusion in GaAs/AlGaAs multilayered structures are investigated by secondary-ion mass spectrometry and photoluminescence measurements. Zn diffusions are performed at 575 degrees C into Si-doped, Be doped, and Si/Be-codoped identical GaAs/Al0.2Ga0.8As multiple-quantum-well structures. The results obtained by secondary-ion mass spectrometry show that the Zn diffused region of all structures are disordered. The effective Zn diffusivity and the disordering rate are enhanced by Be doping and reduced by Si doping. Photoluminescence measurements give information about different point defects in the multilayered structures and the reactions of these defects during the diffusion process. Before Zn diffusion, the Si-doped structure contains a high concentration of column-III vacancies, whereas column-III interstitials may be the dominant defects in the Be-doped structure. After Zn diffusion, we observe a reduction of column-III vacancy concentration in the Si-doped sample and an increase in column-III interstitial concentration in the Be-doped sample. A model based on the "kick-out" mechanism of Zn diffusion is proposed to explain our observations. The incorporation of Zn into the crystal lattice during Zn diffusion results in a column-III interstitial supersaturation responsible for the Al-Ga interdiffusion. The effective Zn diffusivity and the disordering rate are controlled by the background donor or acceptor concentration in the structure and by the column-III interstitial concentration behind the Zn diffusion front. The effective Zn diffusivity and the disordering rate increase with increasing acceptor concentration, but they decrease with increasing donor concentration. Since column-III interstitials and column-III vacancies can mutually annihilate, the concentration of column-III interstitial and column-III vacancy in the Si-doped structures is reduced, leading to a retardation of Zn diffusion. On the contrary, the contribution of the column-III interstitial concentration in the Be-doped structure to the Zn-diffusion induced column-III interstitial supersaturation results in an enhancement of the Zn diffusivity.