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

Scanning tunneling microscopy has been used to study the growth by molecula r beam epitaxy of InAs quantum dots (QD's) on GaAs(001), with specific emph asis on measuring the volume of the dots at different temperatures as a fun ction of InAs deposition. At low temperatures (similar to 350 degrees C), t he total QD volume is consistent with a classic Stranski-Krastanov mechanis m since it is equal to the additional amount of InAs deposited after the tw o-dimensional (2D)-->3D growth mode transition. By contrast, high substrate tempera tuns (>420 degrees C) result in QD's with a much greater volume, a nd the implication is that significant mass transport occurs to the dots fr om 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 cl assical Stranski-Krastanov growth process is incorrect. [S0163-1829(98)5044 8-1].