LAUSR

Abstract A two- to three-dimensional (2D to 3D) transition in InAs/GaAs sub-monolayer quantum dot (SML-QD) growth was investigated, and its evolution was traced. From the AFM results, the SML-QDs disappeared gradually and plateaus around each island formed with increasing GaAs capping layer thickness (tCL) from 1.5 ML to 4.5 ML. The SML-QDs become fully covered with a GaAs capping layer, leading to a planarization process caused by strain relaxation. In addition, when the individual InAs coverage was is insufficient to cause a 3D transition, similar plateaus formed when stacking with an increasing number of stacking layers (S) from 2 to 6. On the other hand, as the InAs coverage was increased from 0.3 to 0.5 ML, 3D dots with a comparable size to typical SK-QDs were observed beyond S = 4. This means that as the total InAs deposition thickness increases above a critical thickness (~2.0 ML), 2D-small islands transform spontaneously into 3D-pyramid QDs. Such structures then show similar optical characteristics to SK-QDs. Overall, the transition from 2D to 3D in InAs/GaAs SML-QD growth could be controlled by careful choice of the parameters tcl, θ, and S.