Sb segregation in ultrathin GaAsSb layers: A quantitative analysis of soaking/desorption stages.

Abstract

We present a quantitative analysis of Sb segregation in ultrathin GaAsSb films (1–20 ML) grown with soaking/ desorption methods. Sb soaking advances Sb incorporation almost to the beginning of the growth, increasing the compositional gradient for all thicknesses. Application of the desorption step alone increases the compositional gradient at the upper interface by removing a fixed amount of Sb but erases layers thinner than 10 ML. When both methods are combined, the Sb balance changes with layer thickness. Thinner layers lose Sb while thicker layers gain Sb. The amount of Sb desorbed is related to the floating layer content at the time of desorption, which varies with thickness. Segregation simulations show that the segregation energy changes during layer growth, being initially higher but stabilizing around the same value for all cases. Sb-soaked samples reach the segregation steady state at a distance of 5 ML from the origin, much earlier than non-soaked samples (10–15 ML). The effect of desorption produces a large perturbation of the segregation steady state, which is much greater in the desorption-only sample than when combined with soaking. The combined effect of soaking and esorption gives the best GaAsSb films with steeper interfaces and no delay in onset.