Porous silicon photonic crystals: Influence of the etch-stop on the optical response

The optical response of one-dimensional porous silicon photonic crystal (1D-PSPC) was investigated as a function of the etch-stop time in the growing of two adjacent layers with high and low porosity. It was found that the characteristic photonic band gap, or even the resonance peak for the case of microcavities (1D-PSPC Mc), undergoes an almost linear redshift trend. The structural and optical analysis of these devices reveals that this fact is yielded by the increment of both etching rate and porosity due to the etch-stop time. Longer etch-stop times allow better HF concentration restitution at the etching front because longer times enable better HF diffusion, reason for which layers with low porosity and thicker thickness are achieved.