In this Work, the potential and feasibility of using structured silicon membranes as an active electro-optical light modulators in the Mid-Wave Infrared MWIR range are evaluated and compared. The near IR pump-Mid IR probe used to investigate spectral, fluence dependence and time dependence optical properties of nano and microporous silicon membranes. The results indicated that the spectral features of both samples is structure dependent parameter including the skeleton dimensions , pore and porosity . Both membranes demonstrated ground state transmission of about 90 % with 60% achievable modulation when pumped at fluences less than 5mJ/cm2. The nanoporous membrane demonstrated response time as fast as few tens of picoseconds allowing its use in the GHz regime, while microporous silicon demonstrated three order of magnitude slower allowing its use in the MHz regime.
The time resolved results indicated that the carrier recombination of the microporous silicon follows Shockly Read Hall (SRH) with recombination coefficient of about 1.65 s-1. For nanoporous silicon, the SRH type dominates the recombination at low excitation fluencies, while at higher excitations, the Auger type competes with SRH and even dominates the recombination process. The longer SRH recombination observed at 3.5 µm attributed to vibrational-electronic state coupling
