Periodic versus aperiodic: Enhancing the sensitivity of porous silicon based optical sensors

The authors have compared the sensitivities of resonant optical biochemical sensors, based on both periodic and aperiodic porous silicon structures, such as the Bragg and the Thue-Morse multilayer. The shifts of the reflectivity spectra of these devices on exposure to several chemical compounds have been measured: the aperiodic multilayer is more sensitive than the periodic one. Adopting a simple theoretical model of the optical response of devices, they inferred that the aperiodic structure provide a higher filling capability with respect to the periodic one, due to the lower number of interfaces.