We outline a procedure to extract the optical-absorption coefficient as a function of energy from measurements of photoconductivity and assess the assumptions involved in applying it to $a$-Si: H. Using this procedure, we obtain accurate absorption spectra in the range from 1.8 to below 1.2 eV. These spectra show an absorption shoulder around 1.3 eV which we analyze in terms of possible optical transitions involving specific distributions of states in the gap.

• Received 3 March 1980

DOI:https://doi.org/10.1103/PhysRevB.22.1918