Electrochemical Engineering of Wide Photonic Bandgap in Silicon Nanostructures for Omnidirectional Mirror Applications

Abstract We report the optimized design and theoretical analysis of broadband omnidirectional mirrors made of silicon nanostructures. The design principle is based on regulating the electrochemical etching process of single-crystalline silicon substrates in acidic solution using train of sinusoidal current waveforms with tightly-spaced frequencies. The individual frequency of the etching current waveform is calibrated to produce a specific photonic band in the reflectance spectrum. A linear relationship is obtained between the frequency of the current signal and the resonant position of the photonic band. The frequency range of the etching waveform is selected to produce a broad photonic peak resulting from the bandgap overlap among multiple photonic bands associated with the individual frequency of each current signal. The transfer matrix method is utilized to calculate the angular reflectance spectra of the experimentally obtained omnidirectional mirrors for both transverse electric (TE) and transverse magnetic (TM) polarization of the incident light. Good agreement is found between the experimental and theoretical reflectivity spectra.