November 5, 2004, Eindhoven, Netherlands--A team of scientists from Philips and the Kavli Institute of Nanoscience are the world's first to successfully demonstrate the growth of III-V semiconductor nanowires on germanium and silicon substrates. In the November 5, 2004 issue of Nature Materials, they present a detailed study of this important step toward integration of the optoelectronic properties of III-V semiconductors with the silicon technology base of the semiconductor industry.
Until now, III-V semiconductors could not be fabricated on silicon or other group IV materials by the conventional fabrication route of thin-film deposition and lithographic structuring. This is caused by fundamental issues such as lattice and thermal expansion mismatch, which prevent a growth mode in which the crystallographic structure of the substrate is copied in the layer grown on top ("epitaxial growth"). This growth mode is essential to produce the required material properties such as a low interface resistance, which is important for future electronic devices such as transistors and light-emitting diodes.
The team solved the problem by growing the III-V material in a "bottom up" approach, i.e. instead of growing a layer over the entire substrate and removing the parts that are not needed, III-V materials, in the form of nanowires, is only grown at substrate locations where it is needed. Because this results in many small individual structures rather than one large connected layer, the mechanical stress with the substrate is relieved easier and perfect epitaxial growth can indeed be achieved.
The key to achieve this type of growth was the use of the vapor-liquid-solid (VLS) method to grow the semiconducting nanowires. In this method, metal (gold) seeds are deposited (using conventional lithography) at the substrate locations where the nanowires should grow. Then the semiconductor material is applied to the substrate in vapor form. The vapor dissolves into the metal seeds, and when this mixture becomes over-saturated, growth of the semiconducting material in the form of a nanowire starts. The team showed that perfect epitaxial growth, with atomically smooth interfaces and low contact resistance could be reached, providing an excellent base to explore these materials in devices such as transistors, integrated circuits and light-emitting diodes.