CARBON-INDUCED GERMANIUM DOTS - KINETICALLY-LIMITED ISLANDING PROCESSPREVENTS COHERENT VERTICAL ALIGNMENT

Pregrowth of a small amount of C on a Si(001) substrate induces small Ge quantum dots. We present a structure where an initial layer of thes e C-induced Ce dots is followed by five layers of four monolayers Ge, each layer separated by a 2 nm thick Si spacer. Although the critical thickness for planar growth of a single Ge layer is not exceeded, a ve rtically aligned stack of Ge islands is formed. If we substitute the p ure Ge layers by a fivefold stack of C-induced Ge dots, no vertical is land correlation is observed. The phenomenon is explained by the stron gly kinetically limited process of C-induced Ge island formation, itse lf. Photoluminescence experiments on stacks of 0.16 monolayers C/2.2 m onolayers Ge dots, where we systematically varied the Si spacer thickn ess and the number of dot layers, suggest that the average dot size in creases if the Si spacer is kept thinner than 10 nm. (C) 1998 American Institute of Physics.