Colorful InAs Nanowire Arrays: From Strong to Weak Absorption with Geometrical Tuning

One-dimensional nanostructure arrays can show fascinatingly different, tunable optical response compared to bulk systems. Here we study theoretically and demonstrate experimentally how to engineer the reflection and absorption of light in epitaxially grown vertical arrays of In As nanowires (NW's). A striking observation is optically visible colors of the array, which we show can be tuned depending on the geometrical parameters of the array. Specifically, larger diameter NW arrays absorb light more effectively out to a longer wavelength compared to smaller diameter arrays. Thus, controlling the diameter provides a way to tune the optically observable color of an array. We also find that arrays with a larger amount of In As material reflect less light (or absorb more light) than arrays with less material. On the basis of these two trends, In As NW arrays can be designed to absorb light either much more or much less efficiently than a thin film of an effective medium containing the same amount of In As as the NW array. The tunable absorption and low area filling factor of the NW arrays compared to thin film bode well for III-V photovoltaics and photodetection.