Credit: © 2007 AIP

Silicon is an extremely inefficient light emitter and this limits its potential for optical applications. However, patterned silicon and silicon–germanium nanostructures emit light much more efficiently than Si thin films, thus raising the prospect of producing all-silicon optoelectronic circuits integrated with standard CMOS technology. Finding simple and inexpensive methods for reproducibly realizing patterned Si nanostructures is therefore an area of intense interest.

Now, Jing Zhu and Zhipeng Huang1 of Tsinghua University, Beijing, China, have synthesized arrays of hemispherical shells of silicon–germanium nanocrystals exhibiting a photoluminescence peak at ˜890 nm with a 700-fold greater intensity than unpatterned thin films. The SiGe shells were produced on Si substrates using a self-assembled array of polystyrene nanospheres as a template. The spheres were reduced in size by reactive ion etching and a SiGe film was deposited by pulsed laser deposition. After heating the Si substrate to 700 °C to remove the polystyrene template and connect the SiGe hemispheres to the SiGe film on the substrate, a further layer of SiGe was deposited at 700 °C.

The SiGe shells were composed of 3.5-nm-diameter nanocrystals with a Si content of 50%. The enhanced photoluminescence intensity was attributed to increased extraction efficiency of light from the SiGe hemispherical structures.