Ge quantum dot molecules and crystals: Preparation and properties

Templated self-organization has been used to prepare two-dimensional arrays as well as three-dimensional quantum dot crystals (QDC) containing Ge dots in a Si host crystal. Si(1 0 0) substrates have been patterned with two-dimensional hole gratings using extreme ultra-violet interference lithography (EUV-IL) and reactive ion etching. The EUV-IL was realized by multiple beam diffraction using Cr gratings on SiN_x membranes fabricated by e-beam lithography. Si/Ge overgrowth was performed by molecular beam epitaxy. The impact of the microscopic shape and size of the prepattern using the mask design and the EUV-IL exposure dose as parameters on the Ge dot nucleation has been studied with atomic force microscopy, transmission electron microscopy and photoluminescence measurements. Adjusting the growth parameters in multiple layer deposition the initial two-dimensional configuration was transferred into three-dimensional QDC.