Composition of InAs quantum dots on GaAs(001): Direct evidence for (In,Ga)As alloying

Abstract

Scanning tunneling microscopy has been used to study the growth by molecular beam epitaxy of InAs quantum dots (QD's) on GaAs(001), with specific emphasis on measuring the volume of the dots at different temperatures as a function of InAs deposition. At low temperatures (\ensuremath{\sim}350 \ifmmode^\circ\else\textdegree\fi{}C), the total QD volume is consistent with a classic Stranski-Krastanov mechanism since it is equal to the additional amount of InAs deposited after the two-dimensional (2D)\ensuremath{\rightarrow}3D growth mode transition. By contrast, high substrate temperatures (>420 \ifmmode^\circ\else\textdegree\fi{}C) result in QD's with a much greater volume, and the implication is that significant mass transport occurs to the dots from both the wetting layer and the substrate. The dots must contain both In and Ga and therefore the description of InAs/GaAs(001) QD formation as a classical Stranski-Krastanov growth process is incorrect.