Fabrication of a Lateral Gradient Rugate in Porous Silicon for a Miniature Spectrometer Application

Here, we report on an application of bipolar electrochemistry utilizing an interfacial potential gradient that is distributed on a silicon electrode to generate a porous silicon film, which behaves as an optical rugate filter with a stop-band that varies in wavelength across the film surface. While the electrode employed is not bipolar because only oxidation is required to etch the silicon wafer, the fundamental concept of bipolar electrochemistry is exploited to generate the anodic current gradient on the silicon anode. When imaged with a smartphone camera and analyzed with the appropriate image processing algorithm, the gradient filter acts as a rudimentary spectrometer. Test spectra are obtained and benchmarked to a conventional CCD spectrometer.