Up till 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 oversaturated, growth of the semiconducting material in the form of a nanowire starts. “Although this process is not new, our team of Philips and the Kavli Institute of Nanoscience was the first to apply it successfully to grow III-V materials on silicon and germanium substrates”, said Dr Erik Bakkers, senior scientist at Philips Research and first author of the article in Nature Materials.

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.

III-V semiconductors are alloys comprising elements from the groups III (e.g. gallium or indium) and V (e.g. arsenic or phosphor) of the periodic table of the elements. Many of these alloys, for example gallium-arsenide (GaAs) or indium-phosphide (InP) are attractive candidates for high-frequency (e.g. high-bandwidth connectivity) or optoelectronic (e.g. integrated optics or LEDs) applications. Until now, devices using these materials are grown onto substrates of the same class, making them rather exclusive and expensive. In the article in Nature Materials, the scientists describe the growth of InP nanowires on germanium substrates. In the meantime, the team has also succeeded in growing InP on silicon substrates, setting an important step towards the application of III-V materials in the mainstream, silicon-based semiconductor industry.

About Royal Philips Electronics
Royal Philips Electronics of the Netherlands (NYSE: PHG, AEX: PHI) is one of the world’s biggest electronics companies and Europe’s largest, with sales of EUR 29 billion in 2003. With activities in the three interlocking domains of healthcare, lifestyle and technology and 166,800 employees in more than 60 countries, it has market leadership positions in medical diagnostic imaging and patient monitoring, color television sets, electric shavers, lighting and silicon system solutions. News from Philips is located at http://www.philips.com/newscenter.

About the Kavli Institute of Nanoscience Delft
The Kavli Institute of Nanoscience consists of 100+ scientists grouped in six renowned research groups and a nanofacility cleanroom within Delft University of Technology in the Netherlands, all aimed at innovative research at the current frontier of science on a nano-scale. Named “Kavli Institute” in 2003, the research groups focus on the physics of nanostructures with emphasis on electronic transport phenomena in individual objects. The nanostructures vary from superconductors to biopolymers and are obtained from nature or fabricated with bottom-up methods or top-down techniques. More information can be found at www.nanoscience.tudelft.nl.

For further information please contact:
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Koen Joosse
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