Critical thickness of self-assembled Ge quantum dot superlattices

In the recent years, there have been considerable attempts to study self-assembled multi-layered Ge quantum dot superlattices for the interest in their novel optoelectronic and thermoelectric properties as well as potential device applications. An interesting feature observed in the multi-layered dot structures was that the dots in the upper layers tended to grow on top of the buried ones, which is attributed to preferential nucleation due to an inhomogeneous strain field induced by buried dots. In this presentation, we show dot evolution characteristics in thick Ge quantum dot superlattices. The study provides strong experimental evidence of the breakdown of the vertical correlation and the growth mode change before and after the reach of the effective critical thickness of superlattices.