Tracing the two- to three-dimensional transition in InAs/GaAs sub-monolayer quantum dot growth

Change in Topography of InAs Submonolayer Nanostructures at the 2D to 3D Transition

“…Comparing these values with those of the three‐stack samples where transition occurred at a total deposited InAs of 2.4 ML, for four‐stack, the transition occurred not at 2.4 ML, but at a higher 2.8 ML. This result suggests that there is no simple critical value in the total amount of deposited InAs, which disagrees with the proposal by Han et al [ 21 ] From the data in the present work, we infer that there exists a critical thickness in deposited InAs per cycle, which depend on the GaAs matrix layer thickness as well as the total number of stacks. Furthermore, the trend of the data suggests the critical thickness to decrease as the number of stacks increases, i.e., 0.8 ML for three stacks and 0.7 ML for four stacks.…”

“…These results suggest the formation of flat 2D stacked islands of InAs, that is widely proposed in SML studies. [ 9,13,16–18,21 ] These samples have the total deposited InAs of 1.8 and 2.1 MLs, respectively. Both exceed the critical thickness in the SK growth of ≈1.7 ML, yet the structures remain predominantly 2D, indicating that these samples are still within the 2D growth regime.…”

“…Note that this illustration is consistent with the common visualizations of InAs SML nanostructures. [ 9,13,16–18,21 ] After oxide desorption at 600 °C, a 100 nm GaAs buffer layer was grown at 590 °C. The substrate temperature was then brought down to 500 °C as confirmed by the transition of the reflective high‐energy electron diffraction (RHEED) pattern from (2 × 4) to c(4 × 4) under our present As 4 flux.…”

“…Due to the large number of growth parameters that can be adjusted, high degrees of controllability and tunability have been demonstrated in SML nanostructures. [ 13–21 ] On the other hand, one of the main disadvantages of the SML growth is the lack of understanding of the mechanisms of nanostructure formation and assembly. Whereas the 2D to 3D transition in SK growth of InAs on GaAs has been extensively studied, and is well understood with a critical thickness of ≈1.7 ML, [ 22–40 ] the transition in SML growth is not yet well explored.…”

“…One recent report that investigated the transition in SML growth suggested the existence of critical thickness in the total amount of deposited InAs. [ 21 ]…”