The doping of hydrogenated amorphous silicon is discussed within the context of Mott's $8-N$ rule, and found to have properties distinctly different from dopants in crystalline silicon. A unifying description of dopant and defect states based on the position of the Fermi energy is given. Some possible consequences of the $8-N$ rule for the deposition and structure of $a$-Si: H are also discussed.

• Received 23 August 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.1187