Strained SiGe/Si quantum well dots and wires selectively grown by LPCVD and their optical properties

To realize quantum dots and quantum wires a variety of approaches are currently being explored. Among the growth approaches there is the selective epitaxial growth using a mask to define the growth region. In this case the feature size and geometry are mainly limited by the lithographic process, With optical lithography we achieved a lateral dimension of greater than or equal to 0.4 mu m. Therefore, to further reduce the lateral dimension, but still using optical lithography, the tendency of facet formation during selective epitaxial growth was investigated. Multiple quantum well Si/Si0.70Ge0.30 structures with Si0.935Ge0.065 spacers and buffers were deposited and characterized by low temperature photoluminescence and transmission electron microscopy. The buffer thickness was varied so as to achieve facet junction. While on large areas the Si0.935Ge0.065 buffer was relaxed, for dots less than or equal to 300 mu m or narrower the structures remained strained even for buffers exceeding by a factor of two to three the critical thickness of large area. In dots and wires where facet junction has taken place a rounded (001) region between facets (approximately 50 nm broad) in the quantum well layers was observed. In wires oriented parallel to [100] sidewalls growth induced wire formation was observed and in addition vertical correlation of these self-organized wires. The photoluminescence of ail dots and wires dawn to the lowest achieved dimension and including the self-organized wires is strong, the integral intensity normalized to the surface coverage by far exceeding that of the substrate related peaks.