Formation and properties of selectively grown Ge/Si quantum dots

Abstract

The selective epitaxial growth of Si layers and Ge quantum dots in windows patterned in oxidized Si(001) was investigated. The selectively deposited Si layers were found to develop towards truncated pyramids limited by {113} facets until the (001) top face disappears. By this way, the Ge dot formation on the (001) surface can then be controlled by adjusting the height of the truncated Si(001) pyramids grown prior to Ge deposition. By monitoring the facet formation during the growth of the Si layers, we showed that it is possible to form single or several Ge dots per window. We have then investigated the formation of Ge dots in stacked selectively grown layers. The Ge dots exhibit a vertical ordering along the growth direction. The optical and electrical properties of Ge dots grown both by selective growth and by self-assembly were investigated. The photoluminescence measurements showed a blue shift of the PL signal from selective Ge dots and the absence of PL from wetting layers as a result of dot size reduction and restricted surface. The forward current–voltage characteristics of Schottky contacts with Ge dots just below the interface exhibit some idealities which can be related to the presence of these dots and indicate that the inhomogeneities are stronger for samples with multilayers of Ge dots.