ATOM-RESOLVED SCANNING-TUNNELING-MICROSCOPY OF VERTICALLY ORDERED INAS QUANTUM DOTS

We present cross-sectional scanning tunneling microscopy (STM) images of strain-induced, self-organized InAs quantum dots grown on GaAs. Sam ples containing 5 and 10 sequentially grown dot layers are investigate d, and dots from different layers are seen to align in vertical column s. Our STM images are in general agreement with previous structural im aging, such as cross-sectional transmission electron microscopy, excep t that dot crowns appear more truncated. Although the size of the dots in most columns is roughly constant, monotonic changes in diameter ar e observed in some cases. STM analysis also reveals many new atom-reso lved details of electronic structure, including dissolution of the InA s wetting layer and the presence of indium between the dot columns, wh ich we attribute to segregation and diffusion of indium out of the wet ting layer during overgrowth. (C) 1997 American Institute of Physics.