Formation of hydrogen molecules in crystalline silicon

Molecular hydrogen was directly observed by Raman spectroscopy in silicon samples subjected to a hydrogen plasma. At lower hydrogen plasma temperatures (∼150°C) the hydrogen molecules form at tetrahedral interstitial sites within the Si lattice. For higher temperatures (>150°C) the plasma treatment results in hydrogen related platelets which act as sinks to which the molecules diffuse. Once trapped within the extended voids created by the platelets, the H2 molecules exhibit a vibrational frequency that is practically the same as the well-known value for gaseous H2.