1 Fabrication of Gas Sensor Device for H2 and NO2 from Porous Silicon

A nanocrystalline porous silicon (PS) layer was prepared by electrochemical etching method of p–type silicon wafer in hydrofluoric acid (HF). The properties of porous silicon structure under various etching times (10–50 min), HF concentrations, and current density were studied. The study included photoluminescence (PL), morphology, x–ray, and gas sensor. The results (PL) spectra (peak wavelength) can be shifted from (505 to 625) nm. PL analysis indicated that the energy band gap can be tuned from (1.984–2.455) eV with respect to etched time. Atomic Force Microscopy (AFM) analysis showed that the PS layer had a sponge–like structure. Surface roughness and the pyramid–like hillocks on the entire surface play an important role in variation visible luminescence. The AFM images shows that the average diameter of the PS layer pore and thickness the Silicon decreased when etching time increase and the average diameter particleboard ranged from (80.8–35.4) nm. PS X–ray topography studies that the skeleton maintained its silicon crystalline structure after anodization. PS Sensors were fabricated and tested successfully on H2 and No2 gas