**4.2. Electronic applications**

Gas sensing, gettering, lithium-ion batteries, and solar cells antireflection coatings are the main application areas of porous silicon in the field of electronics. The large amount of surface area makes porous silicon a promising candidate for realization of gas sensors. Almost a dozen structures have been proposed for porous silicon gas sensors based on alteration of the electrical and optical characteristics of the material in presence of more than 50 chemical species. Porous silicon has also been utilized as an anode in lithium-ion batteries. These anodes not only have more capacity than conventional anodes used in lithium-ion batteries but also are devoid of mechanical instability due to the expansion/contraction problem of bulk silicon with lithiation and delithiation process. Another electronic application area of porous silicon is gettering, i.e., deportation of impurities from active regions of the electronic devices. The great deal of surface area in porous silicon absorbs the impurities and makes the material suitable as a getter medium. Finally, porous silicon is an appropriate candidate to be used as antireflection coatings in solar cells due to its tunable refractive index.
