Effects of background n- and p-type doping on Zn diffusion in GaAs/AlGaAs multiple-quantum-well structures

Abstract

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 °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 diffusion induces an enhancement of Be out-diffusion and the disordering of all structures. The effective Zn diffusivity and the disordering rate are increased by Be doping and reduced by Si doping. Photoluminescence measurements give information about the reactions of different point defects during the diffusion process. Before Zn diffusion, the Si-doped structures contain a high concentration of column-III vacancies, whereas As vacancies are the dominant defects in the Be-doped structures. After Zn diffusion, we observe a reduction of column-III vacancy concentration in Si-doped structures and an increase of column-III interstitial concentration in Be-doped structures. A model based on the “kick-out” mechanism of Zn diffusion is proposed to explain our observations. The supersaturation of column-III interstitials behind the Zn diffusion front is responsible for the enhancements of Al–Ga interdiffusion and Be out-diffusion. The effective Zn diffusivity is controlled by the background donor or acceptor concentration ahead of the Zn diffusion front and by the concentration of column-III interstitials behind the Zn diffusion front. For Be-doped structures, the increase in the background acceptor concentration and the supersaturation of column-III interstitials in the Zn-diffused region results in an enhancement of the Zn diffusivity. For Si-doped structures, the effective Zn diffusivity decreases with increasing background donor concentration. Moreover, the concentrations of column-III interstitials and column-III vacancies in the Zn-diffused region are reduced due to their mutual annihilation, leading to a retardation of Zn diffusion.