Growth of Ge quantum dots on Si ( 100 ) - ( 2 × 1 ) by pulsed laser deposition

Self-assembled germanium quantum dots (QDs) were grown on Si ( 100 ) - ( 2 × 1 ) by pulsed laser deposition. In situ reflection-high energy electron diffraction (RHEED) and postdeposition atomic force microscopy are used to study the growth of the QDs. Several films of different thicknesses were grown at a substrate temperature of 400 ° C using a Q -switched Nd:yttrium aluminum garnet laser ( λ = 1064 nm , 40 ns pulse width, 23 J ∕ cm 2 fluence, and 10 Hz repetition rate). At low film thicknesses, hut clusters that are faceted by different planes, depending on their height, are observed after the completion of the wetting layer. With increasing film thickness, the size of the clusters grows and they gradually lose their facetation and become more rounded. With further thickness increase, the shape of these clusters becomes domelike with some pyramids observed among the majority of domes. The effect of the laser fluence on the morphology of the grown clusters was studied. The cluster density was found to increase dramatically while the average cluster size decreased with the increase in the laser fluence. For a laser fluence of 70 J ∕ cm 2 , dome- shaped clusters that are smaller than the large huts formed at 23 J ∕ cm 2 were observed. At a substrate temperature of 150 ° C , misoriented three-dimensional (3D) clusters are formed producing only a RHEED background. At 400 and 500 ° C , huts and a lower density of domes are formed, respectively. Above 600 ° C , 3D clusters are formed on top of a discontinuous textured layer.