Influence of a pre-deposited carbon submonolayer on the Ge island nucleation on Si(001)

Abstract

Si surfaces manipulated by a carbon (C) pre-deposition have been used to modify the growth morphology of Ge islands. In situ reflection high-energy electron diffraction and x-ray photoelectron diffraction and ex situ atomic force microscopy studies have been conducted for constant C seeding and varying growth temperatures and Ge coverages, with the aim of deepening the understanding of the relevant Ge quantum dot formation. With temperatures ranging from 400 to 600 °C, well structured Ge islands grow in a Volmer–Weber mode as soon as 0.4 ML of C and 1 ML of Ge are deposited. Strongly modified behaviors are nevertheless observed by changing the Ge growth temperature from 500 to 600 °C. By increasing the Ge coverage from 1 to 6 ML at 500 °C, the island height increases at constant density, whereas, at 600 °C, a strong reduction of the density is observed, with a three-dimensional-two-dimensional transition probably due to a partial Ge intermixing in the Si matrix. These different nucleation schemes are connected with varying evolutions of the initial C-related c(4×4) reconstruction.