dangling bonds can act as surface states in electronic processes. In semiconductors Some allotropes of silicon, such as amorphous silicon, display a high concentration of dangling bonds. Besides being of fundamental interest, these dangling bonds are important in modern semiconductor device operation. Hydrogen introduced to the silicon during the synthesis process is well known to saturate most dangling bonds, as are other elements such as oxygen, making the material suitable for applications (see semiconductor devices). The dangling bond states have wave functions that extend beyond the surface and can occupy states above the valence band. The resulting difference in surface and bulk Fermi level causes surface band bending and the abundancy of surface states pins the Fermi level. For the compound semiconductor GaAs, stronger electron pairing is observed at the surface, making for almost filled orbitals in arsenic and almost empty orbitals for gallium. Consequently, the dangling bond density at the surface is much lower and no Fermi level pinning occurs. In doped semiconductors, surface properties are still dependent on the dangling bonds, since they occur in a number density of around 1013 per square centimeter, compared to dopant electrons or holes with a number density of 1014 to 1018 per cubic centimeter which are thus much less abundant on the material surface. Passivation (silicon photovoltaics) By definition, passivation is a treatment process of the surface of the layers to reduce the effects of the surrounding environment. In photovoltaics (PV) technology, passivation is the surface treatment of the wafer or thin film in order to reduce the surface and some of the bulk recombination of the minority carriers. There are two main ways to passivate the surface of the silicon wafer in order to saturate the dangling bonds: field-effect passivation of the surface with a dielectric layer of SiOx, also known as \Atalla passivation", and hydrogen passivation, which is one of the chemical methods used for passivation. Hydrogen passivation Hydrogen passivation is one way to saturate these dangling bonds. This passivation process is carried out by one of the following mechanisms: deposition of a thin film from silicon nitride SiNx on the top of the polycrystalline silicon layer, or passivation by remote plasma hydrogen passivation (RPHP). In the latter method, hydrogen, oxygen, and argon gases react inside the chamber, then, the hydrogen is dissociating to the atomic hydrogen under the plasma condition to diffuse into the silicon interface to saturate