Evolution of Si0.8Ge0.2 quantum dots during Si encapsulation

Surface structure, determined by scanning tunneling microscopy (STM), surface morphology, determined by atomic force microscopy (AFM), and surface composition, determined by X-ray photoelectron spectroscopy (XPS) of 20.0 nm Si0.8Ge0.2 quantum dots formed at 800 degrees C and encapsulated with 0-10 nm of Si at 500 degrees C and 800 degrees C are presented. It is observed that the quantum dot surface morphology changes during the Si encapsulation at 800 degrees C by the smoothing of the quantum dots. The height of the quantum dots decreases faster than can be accounted for from the amount of Si deposited, indicating that there is movement of material out of the quantum dots during the encapsulation process. Encapsulation at 500 degrees C results in a retention of the quantum dot surface morphology with increased Ge segregation compared to Si encapsulation at 800 degrees C. We conclude that the changing surface morphology at 800 degrees C is not the result of Ge segregation but due to intermixing resulting from the tensile strain of Si depositing on SiGe. (c) 2005 Elsevier B.V. All rights reserved.