Photoluminescence in nanoneedles

Silicon is the workhorse among semiconductors in electronics. In optoelectronics, where light signals are processed along with electronic signals, gallium arsenide is the workhorse light emitter—for example in LEDs and lasers—but getting GaAs to cooperate with Si remains challenging. Scientists at the University of California, Berkeley, have now grown GaAs needles that poke out of a Si substrate, and the needles emit bright photoluminescence at room temperature. About 3–4 µm long and tapering at a gentle 6- to 9-degree angle down to tips about 2–5 nm across, needles like the one shown here were grown to match the crystal structure of the Si despite a 4% lattice mismatch where they meet the substrate. Working in Connie Chang-Hasnain’s lab, graduate student Michael Moewe says that he expects the needles to be valuable in several applications including atomic force microscopy; the sharp tips can be grown in arrays without additional etching or processing steps. Delivering light from a sharp tip could allow a targeted examination of the sample and possibly even permit the spectroscopic study of single molecules. (M. Moewe et al. , Appl. Phys. Lett. , in press.)