Optical properties of Si-Ge-C nanostructures deposited by MBE

Molecular beam epitaxy (MBE) has been used to deposit quantum structures in the material system Si-Ge-C in order to evaluate the possibilities for Si based opto-electronics. In particular the growth of Si/SiGeC quantum wells, the growth of quantum structures on pre-patterned Si substrates and the self-organised growth of Ce and C-induced Ge dots have been investigated. Studying the photoluminescence (PL) response of strained SiCeC quantum wells of various compositions and well widths by MBE the band discontinuities for compressively strained and lattice matched SiGeC/Si heterostructures have been determined. The data indicate a type I bandalignment in Si/SiCeC quantum well structures. By modifying the morphology, the chemistry or the strain of Si surfaces the formation of Ge quantum dots can be triggered. The growth of strained SiGe alloys on a small mesa leads to plastic relaxation of the strained film. The degree of relaxation depends on the thickness, the size, and the crystallographic orientation of the mesa. Phonon resolved pi, spectra were obtained from the type II transition between the strained Si and the relaxed SiGe grown on small mesa structures. In addition, the self organised growth of Ge dots on bare and on C covered Si (100) surfaces has been studied. The deposition of 2-4 monolayers of Ge on these surfaces leads to the formation of small, irregularly shaped islands without facets. Intense photoluminescence is observed from samples containing multiple C-induced Ge island layers.