Efficient light scattering by nanowires for random lasers and next-generation solar cells

One-dimensional nanowires from semiconductors like InP, GaP, and Si are promising nanomaterials for next-generation inorganic solar cell devices. Understanding their optical response is extremely important for achieving increased performance in solar energy collection. Researchers at the FOM Institute for Atomic and Molecular Physics (AMOLF) and Philips Research in the Netherlands have investigated strong light scattering in layers of nanowires. Examples of nanowire layers are shown in Figure 1. Using a specially developed broadband optical technique, they show that trapping of light by multiple scattering is important in the design of nanowire devices (Figure 2).

The researchers have demonstrated that nanowires actually can be grown to form one of the most strongly scattering materials available today. Next to its technological relevance, this property opens exciting new prospects in fundamental research on random lasers and Anderson localization of light. By matching the nanowire diameter to the optical wavelength, light can be trapped for several periods inside the nanowire, leading to a resonant enhancement of their scattering efficiency. The high tunability of nanowire properties and alignment, and the general applicability to groups III-V, II-VI, and IV semiconductors, enable new possibilities for harvesting of the solar spectrum.

This work is part of an industrial partnership program between Philips and FOM.

More information: Otto Muskens, present address: University of Southampton, United Kingdom, email; Ad Lagendijk, AMOLF, Tel. (0031)-(0)20 - 6081234.

Reference:
Large photonic strength of highly tunable resonant nanowire materials. Otto L. Muskens, Silke L. Diedenhofen, Bernard C. Kaas, Rienk E. Algra, Erik P. A. M. Bakkers, Jaime Gómez Rivas, and Ad Lagendijk, Nano Letters, published online on 4 February 2009.

Figure 1 High densities of GaP nanowires were grown with controlled sizes and alignment using vapor-phase epitaxy at Philips Research. (left to right) Cross-sectional Scanning Electron Microscopy images of nanowire layers with increasing nanowire diameters.

Figure 2 Using a new technique of broadband enhanced backscattering, the transport mean free path of light in the nanowire medium was determined over a wide spectral range in the visible and infrared. The result, presented in the right panel, shows a strong variation of the mean free path from the weak to strong scattering regimes with characteristic oscillations corresponding to the guided modes of the wires.